No sound device???

I used to play cd while doing schoolwork but even though light blinks to show it is reading cd there is no sound. I can still play cds/dvds but it says no sound device installed. How can I fix it???

Compaq Presario, winxp home, AMD 1.7ghz, 2hd -80gb with 67gb free, 160gb with 136 free.

I’ve had the problem for 6 weeks, would system restore help???