My computer has suddenly stopped playing sound! The last time I had my computer on everything was working fine, now I turned it on and I can hear the introduction sound on the welcome screen when I turn it on, but I went to watch an episode on the internet and there is no sound playing and the little volume icon on the bottom of the screen has disappeared, any help?

When the volume icon vanishes it generally means that you have lost the drivers to your sound card...it happens from time to time.

Go to your computer manufacturer's website and look under support/downloads/drivers for your model of the computer and operating system and find the audio driver and download it to your desktop. Then close out all windows and open the file and start the set-up procedure. After installation restart the computer and the found new hardware wizard will finish reinstalling the drivers and you should be fine.