iMac Late 2012 27" - Black screen - Solid Green LED (bottom)

Aloha, here are the details:

Power switch wasn't putting it to sleep previously.

Froze yesterday, had to unplug to power off.

Current:

Won't power on now, no beeps, no fans, no lights come on.

Solid Green LED showing on the logic board (bottom led) when power cable connected.

"Seems" like the power button doesn't work.

Tried:

Removing screen & RAM - same thing, no fans or beeps on press of button.

Holding button down for 10 seconds - no change.

Green Light on logic board doesn't flicker or do anything.

Any ideas?

Any idea how I can test the power switch?