Odd video prob I don't think is the vid card

First off, I want to thank you guys in being so great in helping me. This site is amazing, as well as the members.

Now, I am trying to repair a computer and have ran into an odd problem that I'm not sure how to diagnose. Upon receiving the computer, the video would turn on when the power button was pushed, stayed on for a couple seconds, and went off. Maybe occasionally blinking back on for a moment. It has done this through multiple monitors so that rules out that and the cable. Assumed that the video card could be going bad. Removed the video card and plugged the monitor into the onboard video. Same issue. Ive now realized if I unplug the cord to the monitor, and plug it back in, I get a flash of the video. Its flashing out during the bios screen. Where should I go from here? I'm assuming it must be hardware. If the video card being removed didn't fix it, the only thing I can think is maybe the mobo? If it was the power supply no longer working properly, wouldn't taking the load of the added vid card off of it fix the problem? Help plz!

And thank you so much for your time in advance