Assuming that you are using Windows XP, go to Start>Settings>Control Panel>Sounds and Audio Devices and check the volume levels under the 'Advanced' button.
Another thing to try would be to press the blue 'Fn' key near the space bar and then adjust the volume level using the top two keys in the top right of the keyboard (both should be marked with a blue speaker).
Hopefully one of those suggestions will bring your speakers back to life!!
Thanks for the reply ...Tried both but to no avail I think i've some virus cause they came to life one day after Mcafee popped up and said it cleared some virus that had effected the sound but two days later it was gone again..tried doing a virus scan but no joy HELP