First, when you restart, does it crash when Windows is about about to restart, or when it's always rebooted.
If it's before it restart, maybe you got a buggy software that crash when you try to shut it down or restart, go in :
Control Panel --> Administration Tools --> Event Viewer, and look at the application event and system event, it should tell you what make you crash, otherwise, if there is nothing, try to shut each program you think that make you crash before restarting or shutting down your computer.
I have the same problem as you, but it only when I'm using flash in full screen mode.