Games Crash On 64 Ultimate

I have a problem with vista 64 ultimate. When i play a game, there is nothing, it never crash or anything. But when i restore games to minimize it half so i can do other stuff, so the game is running in the background on the desktop then it crashes. Like if someone writes a email, and i want to copy the name to a text document, then i restore the game, to get it on the backgroud so i can read the email and write it down. But after 5-10 sec if any game is restored,then my comp crashes.

Once i gotten blue screen of death but it normally goes black screen. Its like vista ultimate 64, cant handle a game running on restored mode, so i can maximize it again for full screen. And that is really annoying. It also shuts out the possibility to play games in windowed mode. If i play a game in windowed mode it dont crash but if i click on a icon like my computer then there is 5-10 sec time before it crashes unless i come fast back clicking on the game again.
Hopefully all get the point of what im saying.