|".... I left it on for a few hours and when I came back to use the computer there was no sound at all."|
Sometimes the sound isn't enabled properly after the system goes into Standby mode and you then get the computer to come out of Standby.
Have you tried re-booting the computer?
If that works, you probably need to load the specific main chipset drivers for your mboard in order for the sound to work properly after coming out of Standby. .
On most laptops the built in sound is disabled when you plug in headphones - are those plugged in?
If you use the headphones port a lot, it has a mechanical lever on the inside of the jack in the laptop that can eventually malfunction, and in that case you may get no sound when you unplug the headphones or sound from only from one channel. In that case try inserting a jack in the headphones port, wiggling it, then pulling it out. If that doesn't help, you may need to replace the headphones jack in the laptop.