MUTE IS STUCK AND WHEN TRY TO CHANGE IT SHOW NO OUTPUT

Go step by step and test.

1. System Preference > Sound > Output > Internal Speakers

Highlight Internal Speakers.

Make sure that Mute is not enabled.

2.Plug in and remove the headphone.

If you see red light in the headphone port or not, plug the headphone

in and out of the port 5 or 6 times to flip the microswitch inside.

Sound output may be stuck in the digital mode.

Try this even if you don’t see the red light.

3. Reset PRAM. http://support.apple.com/kb/PH14222

4. Reset SMC. http://support.apple.com/kb/HT3964

Choose the method for:

"Resetting SMC on portables with a battery you should not remove on your own".

5. Applications > Utilities > Audio MIDI Setup

Audio Devices window

Side Bar

Click the Built-in Output.

Under Mute any of the boxes checked? If so, uncheck it.