I have late 2009 iMac i5 27" but recently I have serious problems with it while booting up (not waking from sleep). In many cases normal boot up is not possible, I hear the HDD starting up but the screen stays black and the machine makes the dreadful loud 9 beep pattern that is SOS in a Morse code (3short-3long-3short). After sending the SOS it turns off, the HDD goes silent. Then all by itself it starts to boot once again repeating the above sequence. What is strange the computer is not completly dead. After repeating the SOS sequence few times (it changes from time to time, it can be 3 times but as well 7) eventually it boots normally and the OS X functions without any problem. If during work I'm only putting it to sleep I have no problem with waking it up. Unfortunately the only reference in Apple's support pages to the 9 beeps is for Macbook Air (which my iMac displaying same issue is not) - http://support.apple.com/kb/ht1221 At this moment I'm sure it is not a RAM problem as it would be signalized by 3 not 9 beeps. But just for sure I cleaned the slots and reseated the RAM. I have also run the Apple Hardware Test (AHT) from the second installation disc and it spit me a following error: 4ROM/4/40000000: 0xb79b9898 I didn't manage to find any reference to AHT Error Code starting with ROM of 4ROM. The second part of the error code is probably a memory adress. I must note that I made all firmware updates at the moment as they were available and they all were applied successfully so I have no idea where this error comes from and why sometimes I'm able to successfully start this computer.