[Numb Nuts]

Heya, I wonder if anyone here can help me here.
My games have recently began to crash my system. Sometimes the computer automatically restarts itself, sometimes doing checkdisk, sometimes not. I know that some games would not work with XP (clean install of XP btw), because they are so old. But others, such as splinter cell, now won't work as well.
I install the game, start to play it, and after a few minutes, every time, the game freezes, and I get a strange buzzing sounds come from my speakers. I have to restart. Other games just restart the computer, with no error message.
This happens with both online and offline games, patched and unpatched. The things is, this has only started to happen recently, I had no problems with this before. Can anyone help?

/edit I have tried this with my normal applications running in the background and all of them closed, no help either way.