Black screen, no power

Hello guys,

So I have a Imac mid 2011 i5 2.7GH/z that dose not power up. I have reset the pram and changed the bios battery out just to be sure.

For diagnostic LED's I get LED1 solid and LED2 will blink once every 4-5 seconds (this causes the fan to power up for half a second).

Note the LED2 is blinking by its self, without the power button being pressed.

I have tested the power button to make sure that its not stuck or anything silly. Also maybe worth noting is that if a usb stick with a light is plugged in the usb stick will flash at the same rate as LED2.

I am unsure as to if this is a logic board or a psu issue and hoping that someone has seen this issue with LED2 blinking with no power button pressed.

Thanks for any help you guys have.