Q: IMAC 2011 - Won't boot & 3 beeps...Apple Novice

According to the following,

Power On Self-Test Beep Definition - Part 2

Your ram is not being detected.  Perhaps you should try reseating them.

What I don't understand is points 5 and 6.  You said you are getting the 3-beeps on boot on the one hand but are able to boot from your recovery partition on the other hand.

If you can boot from the recovery partition I suggest running Disk Utility to repair/verify your drive(s) (not repair permissions).  Also run Apple HardwareTest.

None of these suggestions should effect your data, but if you do manage to get it going make sure you get a back-up plan organised pdq.

Try these suggestions one at a time to see if any one of them resolves the problem. They can be tried in no particular order, but I think I'd try re-seating the RAM after you've tried the other things.

Re-seating the RAM is easy and it should be in the booklet that came with the Mac - but here's my version. Shut down and unplug the Mac, gently lay it face down on a soft, firm surface. With a small Philips screwdriver remove the RAM slots cover which is located on the bottom edge of the Mac (check it in the booklet). There are a couple of plastic tags, pull firmly on them and the RAM should pop out. Press very firmly to reseat the chips. When you think you've pushed them in, just give it an extra firm press, you should sense it fully seating.

Restart using Command R, as already mentioned. You'll be presented with a screen, select Disk Utility. Select your Macintosh HD on the left and then click on 'repair disk'. If it fixes anything click on repair disk again until you get a clean pass. Whilst you're in Disk Utility 'repair disk permissions'. Select Macintosh HD and click on' repair disk permissions'. Restart as normal from the Apple menu.

Try a safe boot. Restart holding down the shift key until you (hopefully) see a grey progress bar. Once booted restart as normal from the Apple menu.

Try an SMC and PRAM reset:

SMC Reset

1. Shut down the computer.
2. Unplug the computer's power cord and disconnect attached devices.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.

Reset PRAM

1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P and R.
   You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

Good luck, and just in case I didn't mention it, get some back-up organised

One additional thing I would add to Paul_31's advice. It would be wise to restart in Safe Mode, this will reset some caches. It is possible one or more cache has become corrupt too so this will clear them. After you have restarted in Safe Mode restart the machine as you normally do.

Also please carefully re-read your owner's manual. What I'm referring to is Apple says:

Smc and pram reset didn't work.  Safe boot didn't work.  Reseating the dimms didn't work.

If you can't boot, short of physically removing the drive, I don't know what you can do.

One thing I am confused about though.  You said "validated and repaired".  Does that mean you were able to boot from the recovery partition which I wouldn't expect?

3 Beeps normally means you have a RAM issue. This can be any one of:

Failed RAM (yes it can and does fail on occasion)

Unseated RAM (remove and reseat)

Incorrect RAM (if you replaced the RAM you have to be careful what you buy!!)