27" iMac suddenly won't turn on… completely dead? (late 2009 2309)

Replace the power supply.

"The ""suddenly won't turn on"" thing happened 2 times before throughout the years (I have it since late 2009...), so every time service would't find anything better than replacing the motherboard - which is f***ing expensive.

So I tried this time what @rudenator suggested, and YES !

In detail, all 4 memory slots were taken. Since some time, I had a doubt about it, as system diagnosis showed up only two ram in place. But so far the iMac worked fine, and I omitted to check physically if I was crazy or if the 2 ram had disappeared somehow.

In reality, the two ""missing"" memory bars seemed to be broken, and yes, they were still in place, they simply didn't show up. These two were in the BOTTOM emplacement. I took them out, as I guessed they were defective since a while.

Next I tried the two remaining individually in the TOP emplacement (relative to the screen which is top). This, because after Apple a single ram can work in the TOP place, but not in the bottom, at least for this model.

THE iMAC REBOOTED with one of them !

Next, I checked them all individually, and in fact even one of the former bottom ram still worked. YES.

I explain myself what happened, by the fact that if you pair a working with a non- working ram diagnosis thinks they are broken both, so if they are in bottom the machine don't shows them, and in top the machine won't boot.

I dont know, but maybe this trying saved me from a new motherboard...(which I wouldn't have paid, as the iMac is 8 years old now), but at least it saved me from buying new ram."

I had the same problem with a late 2009 27 inch imac, thought my display died. After reading this i removed the memory, and placed them back in, and it worked again! Thanks!

"Grey screen, 3 beeps, the grey screen 1 beep, then completely dead not even the sound of the fan starting up. AND THEN.... Just before heading to bed last night I tied again Firstly removing both ram (2x2gb) tried rebooting and although no startup chime I did get a grey screen with the message of 'computer had to shut down previously'. I pushed in one of the ram and the imac (2008 with ssd upgrade) started. I then restarted with both sets of ram and got the grey screen 3 beeps (bad ram from what Ive read here) I then took out the ram that worked and tied rebooting with the one that didn't, grey screen again. So I put the bad RAM to the side and tried restarting twice by placing the good RAM in both slots alternately to make sure it was the ram and not the slots. Once satisfied it was the faulty RAM I ordered a replacement 2gb ram on eBay for £7 which should arrive in the next day or two.

Got up this morning and imac still working fine on the single 2gb.  So after that long waffle I'd say.. simply keep going at it no matter how pointless it seems and you may be lucky.

Ps I forget to mention that when the computer was really dead I was trying numerous keyboard shortcuts and although there was no start up chime it was while holding down the shift key while continually hitting the startup button that got me over the first hurdle.

Good luck - Inky Bob"

"Early 2009 24” iMac 10.9.5 still working beautifully as a platform for Firefox one minute as I walked away from it and completely dead the next when I returned with a coffee.

Unplug, RAM out, vacuum the dust out, plug in to test: beeps and smiles all round.

Unplug, RAM back in, plug and boot: as good as new.

Thanks for the wisdom!"