iMac 24 - first LED lights, push power button, then nothing

Been a PC guy for many years. Decided to cross over and learn some Mac hardwear. Bought an "as is" special, 24" iMac aluminum from Ebay.

Seller stated that it wouldn't power on. I had a good power supply and logic board on the side.

When plugged in with either power supply I get the first LED lit. As soon as I push the power button, it goes out and doesn't come back on, no other lights are ever seen. No fans, no nothing.

Tried the other logic board and get the same error. Any ideas?

Thank you

Dan