Dell XPS 400-Major problems restarting computer

For the past few weeks, I have had a serious problem with my desktop.

If I dare restart my computer, there are lots of colored dots in the middle of the screen when the "Dell" logo comes up. When the computer loads up, I am unable to bring up any application because my screen goes blank for three seconds and my screen shows up after the first "blackout" with icons and the wallpaper "scrambled" - I can move my mouse but do nothing else, and the three second or longer blackouts continue intermittently until I power down.

Sometimes, I am able to get the Task Manager between blackouts (very tough because when you click, the screen blacks out, and it takes three or four attempts between blackouts to click on restart or shut down.

Usually, it takes about 5-10 straight restart attempts before the blackout does not occur again, and I do not restart/shut down for days unless I am forced to when the computer freezes or there is a power surge.

Computer Specs:

Dell XPS 400/Windows XP Media Center
Intel Pentium D 915
1GB Dual Channel Memory; 160GB Hard Drive
Video Card: 256MB nVidia GeForce 7900 GS

Thanks in advance for any assistance! I am sorry my description is not the best - but I hope someone can make out what I am talking about!

^True that. Also have you tried a different GPU?

Eitherway, depending on how much money you have, you can probably get a very good PC (reuse GPU,HDD,RAM) for ~$250-300 (case, PSU,etc)