Hi Jesse, Yes initially the CDF was not there on my machine. uninstalling CDF or installing it didn't make any difference!
But, thanks to Sean. His tip indeed worked out. Instead of deleting the files, I played with the mathpass (licensing file) in the ProgramData folder. I physically entered my license details into it and tried running Mathematica, and lo behold! The activation screen was up. The mathpass in the ProgramData folder had the details of my earlier mathematica (version 6) without being overwritten by the details of mathematica 10 when I installed it (after uninstalling the earlier version). A strange error, but thanks once again to Sean.