iMac beeping 3 times and has a blank screen

@taza Here are a couple things you could try:

1. Try removing the RAM completely from the iMac
   • Does it still give you the same sequence? If so, then try each RAM module one by one to check if it works or not. Maybe one of them doesn't work which would cause the iMac to beep.
   • It's also possible if someone placed the RAM into the slot in the wrong way and damaged a slot, so try the other slots if you suspect one of them doesn't work.
2. Try SMC reset
   • Unplug the power cord, wait 15 seconds, attach the power cord, wait 5 seconds, then power on.
   • It may not work but it has helped for some people
3. If you see a loading bar, then the iMac is probably updating its firmware, which could take a while

I hope this helps :)