Ok, I'm embarassed to admit this, but...
The power cable was loose. Hubby pushed it back in and it powered up fine. Ha!
I did somethine equally stupid regarding my iMac G5. I was using it one day and it died. I figured it was the power supply issue that's plagued Rev A's. So I called Apple Care and they arranged to have a tech come repair it at my house. The morning of the repair my hubby decided to try and turn it on. He noticed the UPS wasn't on. Apparently we got a surge or something and the UPS lost power. He reset the UPS and the iMac started right up.
Sometimes I just assume it's the worst possible problem first, and over look easy things, like power cords and such. Heh.