Power Supply Issue (very strange)

Any help here guys? I have a dell optiplex 390. When I push the start button it does nothing (no lights. no diag code.) but if if press the test (reset?) button and hold it down it will run. Of course it shuts off when I let up off of it. A few times I pressed it (power button) since it first happened and it started up (blue light as "normally" it would before) but then shuts down after a few seconds. I saw this video about how it could actually be the power button itself. (if it helps)

Thanks guys!

https://www.youtube.com/watch?v=6nxMHM3P5RA

p.s. i did exactly everything he did. also I had a 1 GB low profile (no pin connections) card in it and the PSU wasn't that powerful. 250 Watts. Could that be the case. Everything else is stock.

 

Make sure your CD/DVD drive is empty, no stuck CD/DVDs in it. And if you have a multi card reader, ensure no cards are stuck in the slots. There is also a case open switch, even with the case open it should boot up, on some machines it won't boot if the cable is unplugged from the MB.

 

Unplug the power button connector. Short the pins with a screwdriver and see if it starts. If it does, your problem is the power button connector.