Try going into my computer, control panel, hardware, and look for a driver for your sound card. Sometimes the drivers stop working and need to be downloaded again. To do this you will need to know the model of your soundcard and go to their website to download a replacement (which is usually free). Also try your speakers on another computer to make sure its not a speaker issue. Have you checked the 'mute' button on the bottom right corner of your toolbar to make sure it isn't muted. If you see a little speaker double left click it and have a look at the control panel that pops up. you may have to increase the volume sliders.
Stig, November 2008