My sound suddenly stopped working. What can I do to get it back.

1) Check the Volume level:

Simplest of all and often forgotten. If your speakers have a manual volume control, sound can still get muted in the operating system. Go to Start > Programs > Accessories > Entertainment > Volume Control and check the various levels.

2) Check Speakers:

Try your speakers on another system to make sure they are working.

Try another set of speakers/headphones on your computer to see if all speakers fail to produce sound

If the same speakers fail on multiple systems, then it's either the speakers themselves or the wires used to connect them.

3) Check/Update Drivers:

Go into the Control Panel > Sound and Audio Devices > Hardware

Doubleclick your way through your devices and try reinstalling the drivers for each one.