I would go to sysinternals and down load their screen saver. It imitates a blues screen of death and a reboot when active. It is totally harmless I use it as my screen saver. I would then set it up on my machine. Once it is running call him and ask him what the hell he done to your computer. It rebooting all the time. He will either admit that he done nothing or he will try to find the problem. It was my april fools day joke one year.

almost forgot here is the link