Computer died, won't start, tried power supply, still nothing

iMac suddenly went black while using it one day. Powered back up and worked for maybe five minutes and went black again. Powered up another time or two for a few minutes each time and then died for good.

If you are looking at the computer as if you are using it, the right most green diagnostic led lights up when it is plugged in but no others.

When the power button is pushed almost nothing happens. It does sound as though the hard drive spins up, but the fans don't spin, leds don't light up, no thing.

Ordered a new power supply from ifixit and installed it. No change. Same behavior as before.

What else might it be?