my macbook air speaker system has collapsed? i can't play any music or video. what do i do?

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, plug the headphone

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

Sound output may be stuck in digital mode.

3. Reset PRAM. http://support.apple.com/kb/PH18761

4. Reset SMC.

Choose the method for “If the battery is removable”.

https://support.apple.com/en-us/HT201295

5. Applications > Utilities > Audio MIDI Setup

Audio Devices window

Side Bar

Click the Built-in Output.

Make sure that box is not checked under “Mute”.

Make sure that Format is set at 44100.0 Hz.

Right click on the Built-in Output for available options.