Computer wont turn on unless the monitor is off

Hello, everyone! So, I am pretty familiar with computers, and I've built many a computer before, but I have never experienced a problem like this one. It's my girlfriend's computer, a prebuilt IBM ThinkCentre with a Pentium 4 processor. I put a bit more memory in the computer, and I also put a new sound card (not one that requires additional power from the PSU). Lately, the computer absolutely will not start unless the monitor is powered off. If the monitor is plugged into the video card and the monitor is on (the LED is flashing), the computer will start up for just a second before shutting off. The monitor must be off or unplugged from the video card for a couple minutes until the computer starts up, and then it's safe to turn the monitor on. What could be causing this? Any ideas?
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  1. my guess would be the power supply is failing to deliver enough current to the graphics card .
    Is there a secondary power connector to the card? Check that its connected properly
  2. It's strange, though, because the graphics card came stock with the computer, and there's no secondary power connector to the card.
  3. then it may be the power supply is failing, and not delivering enough current to the pci-e slot
    alternatively this could be a motherboard problem
    a graphics card problem

    or a driver problem . Try uninstalling the graphics drivers and then rebooting . Windows should handle the rest
  4. "Lately, the computer absolutely will not start unless the monitor is powered off." meaning that you cannot get the to BIOS if the monitor is on.

    I'd get into BIOS and do the 'reset to defaults' + 'save' routine. The bios may be confused and doign bad thing to the output video device. Once you get past the bios and turn on the monitor then windows is in control of the monitor, not the bios.

    Aside: does the PC totally power off, or does the monitor power off? A bad refresh rate from the PC would knock the monitor down. IF the problem is really the PC then I like the 'failing PSU' theory. To test just download a video demo from ATI or nVidia that is appropriate for your PC's video. If it can run that the PSU is fine.

    Aside: if you can't get into the BIOS with the monitor on that rules out problems with windows. Windows isn't even loaded yet.

    Aside 2: Any chance of a resource conflict between the sound card and the video? Before you do anything drastic try the PC w/o the sound card. When did the problem first appear ? When did the sound card get added?

    Aside3: Any BIOS updates that haven't been applied to the PC?

    Aside 4: Anything unusual around the power management options on the PC in BIOS ? Can you turn power mgt off as a test ?
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