Dell won't boot

I unplugged my Dell Dimension 4600 before a storm, and when I plugged it back in it wouldn't boot. The power light was blinking amber. I pulled it out of the cabinet and took off the periferals.

I had another PSU, so I tried it and no go. The diagnostic lights on the board weren't lit, but the little green light on the board was.
Power light now steady amber, fans on the PSU and CPU run, but that's all.
Tried yet another PSU, no change.
I then disconnected/reconnected everything, tried various combinations with the RAM, no change.
I tried resetting the password jumper.
There are no beep codes coming from the board.

My board.

Anyone have any ideas?
Thank you.