you'll have to rephrase what you are saying, to make it more clear.
but what i THINK your saying, is that you reinstalled windows to clear your hard drives and start fresh, and now every once-in-awhile your computer crashes and then restarts.
does it give you any kind of screen like a blue screen, or just goes black? also, when windows reboots, does it stop on a screen that descibes that windows shut down abruptly, and asks you if you want to start in safe mode?