Q When I turn on my iMac, there are about 8 bleeps and a delay before OS X loads. Sometimes loading fails and it continues to cycle through the bleeps. This started a while ago, but is now more frequent, and less likely to load OS X successfully. What is wrong?

A This is almost certainly a hardware fault. Count the bleeping tones carefully: if they are 3 tones, a 5 second pause, then another 3 tones, it indicates that your memory has a fault.

Other tone sequences that occur in recent iMac models are explained here. If you have AppleCare cover, you should phone to arrange repair. Otherwise you will either need to remove any additional memory that you have installed, to see if that solves the problem, or take your Mac to an Apple-qualified engineer for formal diagnosis and repair.

Updated from the original, which was first published in MacUser volume 27 issue 11, 2011.