Power ?

Once you've had a good long think, start with the basics. Is your computer getting reliable power ?

One tech reported client whose machine crashed every time he received a fax, even though his computer did not even have a modem. It turned out that the client's fax machine was behind him, on a table just out of reach. The client pushed against his desk to push his chair back to reach the fax machine, thereby crushing the plug of his power bar out of the socket. When he leaned forward, the desk moved away from the plug, and the plug popped back into place. Meanwhile the machine had essentially been unplugged and plugged back in again, so it restarted.

The cure -they moved the desk an inch to the left.

Check the basics ! Make sure all of your peripherals are getting good power, too.