Model A1312-100 Serial # C02GF53VDHJP, which is mid-2011 if Duck Duck AI is correct. I bought it new. Hard disks removed, not in the most surgically correct manner, though the drive is back in it. RAM removed. I think the power supply is why it quit booting. If memory serves correct (and it may well not) the fan was beginning to make funny sounds. I haven't used it in probably a couple of years and it's finally time to get it off the desk. I had been using it to run an old printer and a couple of old apps that won't work on the newer Mac I've been using, but didn't need 'em enough to bother getting it fixed.
If you want a reply, include in the subject line "iMac 27 won't turn on". Location is off E St. in Fairview (Hayward).