I am only guessing, but I believe that part of your problem is that you are trying to take the determinant of a desktop published MatrixForm. A MatrixForm is not a matrix and you cannot do any calculations with that, you can only display it.
The last three lines of your post are also unclear exactly what calculation you want to perform.
Can you make any sense out of this reformatted version of your code and describe exactly what calculation you would like to perform?
In[1]:= ClearAll;
M = {{1.1629464285714284, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 1.1629464285714284, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.3258928571428568, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1.1629464285714284, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1.1629464285714284, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2.2204460492503131*10^-16}};
Ke = {{a, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, b, 86831.960212348175, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 86831.960212348175, c, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{-1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, 3508944.3378119003, 0, 0, -1754472.1689059502, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, 63998.987949216324, 0, 0, -31999.493974608162, 86831.960212348175},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, 0, 628325.71209213056, 0, -86831.960212348175, 157081.42802303264},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1754472.1689059502, 0, 0, d, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -31999.493974608162, -86831.960212348175, 0, e, -86831.960212348175},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 86831.960212348175, 157081.42802303264, 0, -86831.960212348175, f}};
Kg = {{0.27639155470249521, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0.77389635316698657, 0.10000000000000001, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0.10000000000000001, 5.6079861111111118, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{-0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.36852207293666028, 0, 0, -0.18426103646833014, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.44222648752399235, 0, 0, -0.22111324376199618, 0.10000000000000001},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, 0, 1.4472222222222222, 0, -0.10000000000000001, -0.18090277777777777},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.18426103646833014, 0, 0, 0.66333973128598844, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -0.22111324376199618, -0.10000000000000001, 0, 0.90656429942418426, -0.10000000000000001},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.10000000000000001, -0.18090277777777777, 0, -0.10000000000000001, 5.7888888888888888}};
Freq = 2*Pi*{7.9044500376256508, 15.974163372274155, 24.288032059533016, 32.770732855521864, 41.136038911151424, 43.063079263399032, 48.785402523448269, 54.598718766416326, 75.177735684082492, 81.001463008934209, 88.775376098692746, 134.97971202269417, 178.59878617099415, 217.08380692586999, 248.25631868168185, 270.08309952191433, 287.32028931433803, 384.15152467225192};
(*K=Ke+T*Kg;
sol=K-(((Freq[[2]])^2).M)*)
In[6]:= Det[M]
Out[6]= 3.25429*10^-136
In[7]:= Det[Ke]
Out[7]= -(1/(-7.53979*10^9 + 31999.5 c))
5.42819*10^-107 (9.45082*10^56 - 6.28449*10^50 a - 6.28449*10^50 d + 4.09369*10^44 a d) (2.76075*10^205 - 8.64833*10^200 b -
2.18163*10^200 c + 6.8334*10^195 b c + 4.28628*10^194 c^2 - 1.34239*10^190 b c^2 - 8.64833*10^200 e + 2.70916*10^196 b e +
6.8334*10^195 c e - 2.14038*10^191 b c e - 1.34239*10^190 c^2 e + 4.20414*10^185 b c^2 e - 1.00994*10^200 f + 3.16298*10^195 b f +
7.96178*10^194 c f - 2.49326*10^190 b c f - 1.55991*10^189 c^2 f + 4.88436*10^184 b c^2 f + 3.16298*10^195 e f - 9.90587*10^190 b e f -
2.49326*10^190 c e f + 7.80768*10^185 b c e f + 4.88436*10^184 c^2 e f - 1.52937*10^180 b c^2 e f)
In[8]:= Det[Kg]
Out[8]= 7.31144*10^-8