My iMac 2390 won’t turn on

My sons 2010 imac 27” hasn’t been turned on in 5 years. Worked before that. I turned it on today and nothing turned on. I removed the lcd screen to gain visual access to th diagnostic LEDs and saw the number 1 LED was on. I pushed the power button and the number 2 LED blinked and then both 1 and 2 shut off. I removed power and repeated only this time I shorted the power switch on the board and got the same result.

I tried holding the power button for 1 min with and without power cord and no change.

Given that it worked before not using it it for an extended period I’d be surprised if the power supply board went bad but of course it’s possible.

Anything else I should try?