iMac G5 20" Model A1145 Dead Nothing on Start-up

iMac G5 20" Model A1145

I have no problems with it overheating or fans making a lot of noise or any of that. After a power went off for the afternoon, When it came on again my imac was dead. I suspected it to be the power supply.

Tested, lead, fuse. Reset PMU/SMU. Nothing. Took front off and the diagnostic LED number #1 only shows. When the power button pressed no flicker of LED#2.

Is this likely to be the power supply?

Or is it the logic board fried?

Your help would be most appreciated.