Suggestion 1:
This is unlikely to be down to the CD drive, but just to test, take it out and try again? Post results here.
Suggestion 2:
Look in device manager. In Windows XP, bring up the properties for My Computer -> Hardware -> Device Manager. Do any devices have warnings or errors (it'll automatically expand the branch of ones that do so you can spot them)? Is you soundcard still listed under Sound, video and game controllers? Post results here.
Suggestion 3:
Is your soundcard an onboard one? If so, have you been playing around in the BIOS and accidentally turned it off?
Suggestion 4:
As pab has suggested, find the correct output and/or turn on your speakers. If this is the cause, hit your head on the desk. Hard.