"Try one RAM stick one at a time in each slot and see if you can identify the bad slot or stick or both. Is the Power on LED flashing?
'UPDATE3/31/17
My answer is incorrect.
See the answer given by onlymyprivatemail
Three long tones, three short tones, three long tones: EFI ROM corruption is detected, and the computer is in EFI ROM recovery mode.
Newer computers automatically recover from a corrupted ROM; when this occurs, a progress bar appears on the screen during ROM recovery mode. Don't disturb your Mac while the ROM recovery takes place. When recovery is complete, your Mac restarts.
If you need to restore the EFI ROM on certain Mac computers produced before 2008, you'll need to use a Firmware Restoration CD to restore the EFI ROM. Search Apple Downloads for the right CD image for your computer."
"Here is a note from the Apple website mentioning specifically about the ""3 long beeps, 3 short beeps, 3 long beeps"" combo beep tone. I could NOT locate any Apple reference to ""3 short beeps, 3 long beeps, 3 short beeps"". These two tone combinations are clearly not the same.
""Mac computers: About startup tones
Learn about the different sounds your computer makes when it starts up and what they mean.
Mac computers can produce several sounds when starting up. Your Mac should produce the familiar single tone on start up. If you hear another tone it can indicate problems with your computer.
1 tone, repeating every 5 seconds: This indicates no RAM is installed.
3 successive tones, a 5 second pause (repeating): This indicates RAM does not pass a data intregrity check.
1 long tone while holding down the power button: Indicates an EFI ROM update is in progress on a computer manufactured before 2012.
3 long tones, 3 short tones, 3 long tones: Indicates EFI ROM corruption is detected and the computer is in EFI ROM recovery mode.
Should you need to restore the EFi ROM on certail Mac computers produced before 2008, you'll need to use a recovery CD to restore the EFI ROM. Newer computers automatically recover from a corrupted ROM; when this occurs a progress bar appears on a grey background. Do not disturb the machine while the ROM recovery is taking place. It will restart back into OS X when it restarts. For more infomation on EFI ROMs, see EFI and SMC firmware updates for Intel-based Macs."""
I work in a computer repair shop and had an iMac brought it with this same problem. I tried multiple sticks of RAM in both memory banks and nothing was working. I swapped out the internal coin battery and it started booting no problems.
Thomas, I don't know if you got this problem resolved yet, but in case you haven't, maybe this will help: I'm currently trying to diagnose an Intel-based iMac, Mid-2007 2.0 GHz model, which is currently playing the same symptoms as yours is/was--the same error beep sequence, kernel panics, runs sometimes, etc. I managed to get the Mac to run long enough to allow me to install a thorough memory testing utility called Memtest onto its hard drive, which you run in single-user mode at startup. It kept displaying RAM errors, even with known-good RAM boards, so I felt it was likely there was a problem with the RAM-controlling circuitry on the logic board. So, I ordered a replacement logic board. That didn't help. Swapping logic boards with the supplier requires that you first remove the CPU and GPU chips before sending the supposedly bad logic board to them, and installing these chips onto the replacement logic board, so the only remaining part from the Mac I'm working on, that's likely to be the cause of the problems, is the CPU chip (the GPU is unlikely, especially since in these earlier iMac models, it doesn't access the main RAM bank). If you haven't already spent money on this, I'd recommend trying a known-good CPU before you try a logic board--it's cheaper, and with these particular symptoms, more likely to be the CPU. Prior to working on this Mac, I'd never seen a bad CPU cause RAM errors, in 23 years of working on Macs. But the way statistics works, is that a number of other techs have probably seen this problem several times in fewer years, especially with some Intel iMac models, which I suspect were assembled with flaky processor chips that failed after a year or two.
