Blurry screen at start-up

Hi there,

I have 10 compaq c400 desktop machines with Win2000 installed.The 2 of them have developed habit of getting blurred, distorted start-up screen when powered on/restarted. The first part of boot is O.K., it is the part when username and password should be entered, that the screen goes berserk and nothing can be done. Usually it will boot up normally after restarting it 3-4 times. All 10 machines are being installed using Symantec Ghost, and I wonder whether it is something to do withthat. Anyone any suggestions?

Thanks