iMac doesn't Power ON / No power, no fans...noting

Hello,

I have an iMac 21.5" 2010 with an i3 3.06ghz processor. Currently when pressing the power button it does not do anything at all no sign of life. I have already verified the power outlet works and tried a known working power cable still noting.

So i opened it up and looked for the LED diagnostic lights, while the power is plugged in all 4 LED lights are off. So i unplugged the power cable and plugged it back in again. LED #1 turned on for about 1/2 of a second then turned OFF.

I looked up the power pin out and found a link to a website that shows the power pin out so i tested PIN #4 which i got a reading of 12V and according to the apple service manual this LED light is supposed to stay ON all the time as long as the power cable is plugged in.

So what could be the issue? Im getting 12V but the LED light is still OFF and only comes on for 1/2 of a second. Is it possible the power is bad if so why do i still get a 12V reading? Or is the logic board bad?

Anybody have any tips what else I can test to determine exactly what the issue is?

Thank you