iMac Not Booting - Fan spins then stops - LED 2 blinks

Hello, my iMac appears to be having hardware issues. I thought it was a power supply issue, so I bought one from this website, but I'm getting the same issue. LED 1 lights up and stays lit, LED 2 blinks 1 time, LED 3 and 4 both do not light at all. Also, when LED 2 blinks both fans spin for about 3 seconds, then stop. This process never stops as long as the power cord is plugged in to the wall. Ive tried all the typical fixes, reseated RAM, reset SMC, pram, and replaced the power supply. I'm thinking it's the logic board, but I can't find anything online with these same symptoms. Any input would be much appreciated. Thank you