Windows 2000 Pro Start Up

I have a COMPAQ EVO 300 SERIES MICROTOWER. iT IS RUNNING WIN 2000 PRO. It has a problem when starting it up. After it post and the windows screen comes, when it switches vga to its hi-res display mode, or when the sign on screen appears. Just moments after that window comes up the screen switches to having these orange/yellow shaded and black vertical lines, and it locks up. ctrl-alt-del wont work. It has to be turned off by holding in the power button or unplugging it. ANyone know how to fix this problem??