Why do I have no sound on my computer?

Maybe Troubleshooting issues with no audio from built-in speakers on Macs - Apple Support can help?

See if creating a different login on your Mac, and then logging into that login has sound.

There've certainly been cases where the hardware is bad, or where the speaker jack has failed.

If you're really on an iMac G5 — and that's probably running OS X 10.5.8? — then this could well be a hardware problem, too.

despite all the advise of endless restarting computer the problem is probably the audio jack. insert jack and twist. you might have to do this a few times to get it right. it's a design fault which apple wont recognise .