@karan
Is it a pirated or Original version bro ?? Also wat are ur system specs and hv u installed any Mods for the game ??
Hv u verified ur game cache ?? if not then do it here:
http://members.optusnet.com.au/fsjk85/Validate/ or u can simply go to steam, my games, css, properties, verify...
please post ur results...
Cheers n e-peace.....