Dell 8600 randomly freezes & goes fuzzy then black

I have a Dell 8600 running windows XP Home w/ SP2. About a month ago it froze up and the screen did something I've never seen before. Everything had a slight double image that was "static-y" - it made stuff look fuzzy; then the screen went black. This began happening maybe once or twice a week, but the frequency has increase to where now it's happening many times a day.

I have to completely shut the computer down and reboot it. I haven't noticed any sort of pattern and I can't remember it happening right after I installed anything new. It's not always the same either - sometimes stuff will go fuzzy and I can't do any operations, but I can move the mouse for a few seconds - then it completely freezes. Other times the screen goes black right away except the mouse is an hourglass, but it won't move, then the screen goes black.

This is driving me crazy and it happens at very inoportune times. Can anyone please help me?!