1) Screen just freezes
2) System does a cash dump.
3) Computer just restarts automatically.
4) The screen image is replaced with multicolored lines going in every direction.
I should note that once the computer starts running well for over 5-10 minutes, it will not crash and run perfectly from then on. I'm pretty sure it's a hardware problem, but not sure how to diagnose exactly what. Any feedback would be greatly appreciated.