My computer has no sound!!! :-(

When you say no sound, do you mean its as if the speakers weren't turned on, or does every media based program throw a major wobbly every time you try to open and play something.

It's as if the speakers weren't turned on. I can play videos but there's no sound and youtube works silently. The volume control icon that's normally on the bottom taskbar has gone and when I go on audio devices in control panel it just says no audio device. When I try and play stuff on WMP I get this message:
Windows Media Player cannot play the file because there is a problem with your sound device. There might not be a sound device installed on your computer, it might be in use by another program, or it might not be functioning properly.

You may have to re-install the drivers, it shouldn't do any harm, unless you don't have the CDs.
Also, is this an on-board sound card, or a seperate one?
Do you have an on-board sound card that is trying to muscle in on the sound card front, despite being told not to.

failing that, find an error code and google it.
I suddenly feel dirty for using the proper noun 'Google' as a verb

My computer did this once when I installed a game that it couldn't support. Removing the game seemed to help, so maybe it's something you recently did?

I found a system restore to a point where my sound did work solved the problem for me. Maybe it'll work for you too

Cheers guys. I'm always reluctant to do system restore unless it absolutely needs it but I went on the manufacturer's website and found the appropriate sound drivers for my model, which seems to have done the trick. Not being able to play music is downright horrible

Is it an addon (PIC or PCI Express) sound card or a chip on your motherboard, if it's the former I'd suggest a re-seating procedure (open case, take card out, put card back in, close case).

If it's the latter I'm having similar problems with the C-Media chip on my Asus M2N-E SLI (/me waits for people to realise I have a gamer box amongst my collection and for the subsequent fainting), it sometimes fails to appear at boot. I solve this by turning PC off, *disconnecting the power cable*, having a cope of coffee and trying again.