I agree with matt about the power supply. I had this machine loose part of the AGP slot. The machine had a high end video card and the monitor stopped working. I put the video card in another machine and it was fine. I then replaced the card with a low end model and everything worked fine. A year later it's still working. I could only conclude that the AGP port had lost some of its power or working capability. If this is your case you can put in a PCI video card instead of the AGP and all should be well.