Any ideas on the problem with my iMac?

[pokari]

I have an iMac Intel (early model). I was using it yesterday and pow!!! it quits on me. It seemed like the power was turned off on the computer. It was a little to get it restarted but after two or three times it did. It worked fine for a little bit and then POW!!! again, it just quits on me. These crashes were when i was running different application. After another time of this happening I keep it off all night unplugged. I then restart it again and after a few minutes(maybe 10 or so) it quits and crashes. I call the Apple help desk and after resetting PRAM, repairing the HD, and running Tech Tools the tech says it is probably a hardware issue. Now the light on the bottom right corner of the iMac comes on but the monitor will not.

It sounds like to me like the logic board. Any other suggestions?

pokari