Guessing it's probably something to do with a corrupted .sys file, but thats a very long shot unless of course you give us more details.
Useful details would be system spec, at what point it crashes (during boot-up? after windows 'loads?'? during gameplay/intensive applications?
All helps
As a suggestion try booting into safe mode, you can do this via tapping F8 on boot-up, and select safe-mode from the menu. This will help because if its still crashing you can rule out any sort of driver corruption/hardware conflict and points to something within the OS, or possibly a virus.