The reboot on crash is enabled. Try disabling that so you can see the crash. Also, you must check the event viewer.
And another common cause. Accepting drivers from Windows Update.
More at http://forums.techarena.in/operating-systems/1140101.htm
Bob
A friend has a computer with Windows Vista (32-bit) and after it's shutdown via the windows start button it starts back up after a short period on it's own for some unknown reason. Can someone give some insight on this matter. Thanks, Gary

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic