How can I stop my computer from freezing?

Like the description says, my computer randomly freezes on me and I have no idea why. I happens 9 times out of 10 when I'm playing a game (any game), but on those rare 1 out of 10 times its when I have Winamp, Mozilla, or any other program open. My first idea was that it was a software problem so I had my computer completely reformatted, but it still freezes. By freezing, I mean just that. As a more in depth description everything, no matter what I'm doing, stops mid stride. I can't move the mouse, can't open anything up, (if I'm playing a game) nothing on my character moves, music cuts off, and I can't even go to the desktop or do the whole "Crtl+Alt+Delete" thing either. Its just frozen in place and all I can do is manually restart it by either flipping the power swith in the back or by pressing the restart button upfront. My next idea was to get a new mother board but, frankly, I don't have the money right now. I don't get online with that comp, so I know it's not spyware or a virus, and I've even updated to the most recent driver for my videocard. So if anyone... ANYONE at all has any insight as to what might be going on I would Greatly appreciate it.