iMac won't power up - likely diagnosis?

I have a 2006 iMac intel 17" (model 1173). My daughter unplugged it while on a while back and it has refused to turn on ever since - no noises, no grey screen, nothing. If it is plugged in and I put my ear to it, there is a faint and somewhat erratic "ting" sound. I can't hear anything when I press the power switch. I have tried to no avail

• a different AC cord
• reseating the ram

It seems likely that the power supply is the culprit, but are there other possibilities to consider before I spend the money on a new supply? Is there a way to test the PSU without opening the unit up (doubtful, I know)

Update - I followed the instructions in the power supply replacement section, and disassembled the imac. In the process I tried powering it up to see if any LEDs on the logic board lit up. None did. I removed the power supply and tested it - it's output was a little over 7 volts - way under spec. So I'm assuming this is the culprit, although it's possible that when it failed, it took something else down with it.

One other note - my particular model is a 2104, which has a different power supply than the one in the instructions for 17" intel iMacs, which I think uses a 2114. The 2104 has a smaller PSU plus a separate DC-DC converter board. The 2114 has both parts on a single board.