sounds like a diagnostics problem,heres how to test it
1.Go to the control panel and select "system"
2.Then go to to "device manager" at the top
3.Click on "display adapters"(under display adapters it should say your video card,then click on it)
4.And some where at the top of that window it should say "diagnostics" click on it
5.There will be a little box with all the diagnostics tests click on one of them and hit "run test"
6.It will do a bunch of weird patterns and stuff DONT BE ALARMED
once its finshed a window will pop up saying if it passed or not
7.Run all of theese tests IF ONE FAILS RELOAD YOUR VIDEO DRIVERS