Computer won't boot, fans flicker for split second and cut off.

There was no warning that anything was wrong it just happened one day. I go to turn on my PC and nothing happened. The lights in the case flicker and fans twitch a little but and then nothing. My friends and I tried a few different thing and only one thing worked, which was removing my graphics card completely and only use an alternate video card that only has a VGA port. Then and only then would the computer turn on, and it worked fine, with the exception of not running high demanding games.

We were convinced it was a failing PSU and it didn't have enough juice to power my card. So we plugged in a 500W PSU. It was only 50W less than the original PSU so we figured it'd work. Same thing happened. Would not boot unless the Video card was unplugged. So we are just stumped, and could use some help.

Our only thought is that 550W was barely getting me by in the first place so at the first sign of failure it just can't power my computer.

Now I already ordered a 750W PSU because I plan on upgrading my graphics card and RAM soon and will probably need a new one anyway, but I'm fearful that this problem will persist even with the new and improved power.

Last resort is taking it to a local PC repair shop but they're notorious for being a-holes about stuff so I want to avoid this if possible, or at least go in know what wrong.