Power Supply Replaced but Still NO POWER

My parents have an iMac 21.5" EMC 2428 that powered down while running one day and never powered on again. I opened it up and no LED's, no noises, nothing. I was convinced to change the power supply so I did following iFixit's guides and power supply (614-0445). Once I changed the power supply and plugged it in LED 1 is on and there's a faint noise of something running which previously there wasn't. When I go to push the power button to turn it on nothing happens, just the LED 1 and the noise of something running which continues until unplugged. Tried PMC reset and nothing. Is this the logic board? Bad power button? Anything I could fix possibly?