Hmm it'd be nice if you would have included as much information with your post as you could have but oh well..
First off it doesnt have to be your video card but it probley is if you just switched over from the ati.
Try changing some bios settings (usually can get into your bios by pushing delete while your computer is booting). Try loading defaults and if you have a normal and optimal video settings mode try both and see what happens. Everything you do in your bios can be fixed easily and you cant harm anything so experiment with settings.. but try to stick with video card related ones such as video rom caching ect.
After that, if you cant get any success, try formatting your hard drive and reinstalling windows. It could be a driver problem or some other software on your hard drive.
Next I wouldnt know what to tell you besides just junk the computer and wait for the new DDR athlon mainboard to be available.. if you upgrade to a AMD thunderbird you will wonder why you bothered to trouble shoot that intel anyway.