Video Gone

I’ve got an old Gateway P5-75 that suddenly stopped sending a video signal. I’ve ruled out bad components and still can’t get a video signal. I’ve tried both the PCI and ISA slots and can’t get the video to show up on the monitor. The monitor knows it is hooked up because I don’t get the “no signal – check cabling” error. Any idea what might have gone bad to cause the video to stop working? All of the components work in a different computer, so it must be something with the motherboard….