you would notice if it would be Windows XP x64 because nothing is compatible with it, you can't run almost anything on it ;)
I had similiar problem with Call of Pripyat, updating driver didn't help but I noticed that when I played it on 1440x900 res it went black for a second from time to time, changing resolution fixed the problem but this might be whole different problem.
Restore game settings to default, if that doesn't help, reinstall GFX driver and PhysX driver.
just some basic advices.
btw. does it occur on any other games ???