Try pressing-- fn and the up-arrow key with a ampifier sign on,or, on the bar at the bottom of your screen there will be a little logo of an amplifier,click that and a sound slide will appear,try that. If that doesn't work Check your settings,by going to-- start-all programmes-Accessories-entertainment-Volume, and check all the slides are at the top. Anything more complicated and i'm lost
Away at the bottom right of your screen, next to the time, is there a picture of a speaker? click or right click on that if it looks to be muted.
Failing that, go into the control panel (Start > Settings > Control Panel) and double click on the "sounds" settings in there. Have a nosey to see if there's anything amiss.
Or just turn the power on your speakers back on :-)
If you go to control panel - sounds and audio devices - adjust the system volume. theres a mute button, if it's crossed then theres the problem. Sometimes this happens to me for no reason.