your windows might be corrupt or virus
or it maybe a pirated. product
try reinstalling windows with original disc
REMEMBRER!! - if u want to save ur data dont change partition while reinstalling widows
when u are installing windows , it will ask that 'on which partition do u want to install windows'
or something like that chooseC drive ,, then it will say that previous windows data will be moved to windows backup (or something..) folder
hit ok and wait till it installs
Always buy original product
and if ur current corrupted window is original then contact microsoft.