The past month, a computer has not been powering on as expected. First, the monitor wouldn't click on, but the keyboard LED's would light up. If I turned off the power supply, the Back ups unit, or the power surge connector then turned them back on, the computer would power on and work well for a week or two. If the computer was left on overnight and then told to restart, it would not restart. We would have to turn off all of the power sources and try again. This past week, I realized that if I disconnect the monitor from the video card and reconnect, then the computer will start up. Today, however, the monitor would start up and then go black as if in sleep mode after 1 minute. I would have to turn off the computer again. I have removed the video card and checked for dirt and dust. Then I put the card back in. I have also switched monitors. Nothing has changed. Is this a video card problem or power supply problem or something else? Does anybody have any ideas? Thank you for your help.