What is wrong with my computer?

My computer running windows xp sp3 suddenly freezes. It will boot up to the login screen and I can sign in but not soon after it starts to boot up, my monitor suddenly indicates there is no signal and goes to standby and the keyboard goes unresponsive (no change in num lock, caps lock lights; attempted keystroke windows shutdowns and restart commands do not respond) I tried using a different monitor, no change. I tried booting from a fedora 13 cd, still no change. Thought about a graphics card failure (using a PNY nvidia geforce 7600 gs, agp) but why would a graphics card failure cause the entire system to freeze, shouldn't it just function regularly? Any help would be greatly appreciated.