I'm not sure why the reason for my sound not working is but in the Device manager there is a problem with a new, audio compatibility driver because it has a yellow exclamation mark beside it.

Under the device status it has written:A driver (service) for this device has been disabled. An alternate driver may be providing this functionality. (Code 32)

There may be a conflict.
Check for any other (sound)drivers and disable.
Then reboot..

what does it mean by reboot and how do I do this?

Is the sound ok few days ago?

If its ok, maybe some programs may be conflicting with your audio driver.

Try using the System Restore to restore to the restore point that you know where your audio driver doesn't have any problem.

The sound was working sometimes, I just had to turn the computer on and off again then it would work, but now it's completely failing to work.

sorry I'm not sure where to find system restore?

Programs/accessories/System Tools/System Restore.
Choose restore to an earlier restore point.
Reboot means to restart.

okay that did not work, system restore only added the days when I went on it which was yesterday and today on the calendar so I cannot pick from an earlier time, I don't know what to do? Any suggestions appreciated.

Do you know what is the audio driver name of your Desktop/Laptop?
Are you familiar about Realtek, Avance, etc.?

Tell me your Audio Driver's Name and i'll give you a site to download your driver and reinstall it to your Destop/Laptop.