What input have you tried?

This really does not appear to be a question about Mathematica. A perusal of the Documentation Center page for Solve should give an indicatation of why I say that.

See Quintic function:

Solving linear, quadratic, cubic and quartic equations by factorization into radicals can always be done, no matter whether the roots are rational or irrational, real or complex; there are also formulae that yield the required solutions. However, there is no explicit formula for general quintic equations over the rationals in terms of radicals; this is known as the Abel–Ruffini theorem, first published in 1824, which was the main motivation of the introduction of group theory by Évariste Galois, a few years later. This result also holds for equations of higher degrees. An example of a quintic whose roots cannot be expressed in terms of radicals is $x^5-x+1=0$. This quintic is in Bring–Jerrard normal form. Some quintics may be solved in terms of radical. However the solution is generally too complex for being used in practice. Therefore, one commonly uses numerical approximations of the solutions, which can be provided by any root-finding algorithm, and in particular by any root-finding algorithm for polynomials.