Boot into "Safe Mode" - change the resolution on the PC.
Then reboot and see if it helps.
I had this happen to me before.
Please help troubleshoot. I had an electrical problem, although I have a powerful surge surpressor with a back up battery. Once I tried to boot up my computer, the monitor flashes on at each step, boot, loading xp and then the desktop but quickly goes off. If I push the power button it will flash on very quickly but will not stay on. What could this be. When I do push the button the picture is clear and there are no error messages on the screen. Thanks