For over last 8-10 months, I've never used the internal speakers on my iMac. Why? Because the internal speakers in a Mac can never match the awesomeness of the Audio Engine desktop speakers I got. I've hooked my AudioEngine speaker set to the headphone port of iMac and never take them out. But a strange thing happened today - there was no sound from the speakers. So I unplugged the headphone jack and was surprised that there was no sound from internal speakers as well. Upon researching, I found out that the the problem persists with a lot of mac devices. I suspect that it's a software related issue; but thankfully there's a fix! All you need to do is - Finder -> Go -> Utilities -> Audio MIDI setup (double click) You should see 'Built-in Output' listed. click on the 'Output' and make sure that the volume levels are somewhere midway on the scale. Use your keyboard to increase the sound volume and play some music file. You should get sound from your internal speaker set. If this doesn't work - it's time for you to take your mac to the Apple servicing center. If you have other tips to fix this problem, please contribute them for the benefit of fellow Apple users.