I posted this to the wrong thread first...

System will no longer play Cds; they 'start' and look like they are playing and even count, but no sound thre the speakers. Tried both RealPlayer and WinAmp.
I can still play mp3s I've downloaded off the net but not store-bought Cds. Oh, yeah...the headphones on the front of the cd-rom work fine. Help?

This is probably too simple to be helpful, but....

Have you checked the sound settings from the icon in the lower right hand corner of your screen (assuming your task bar is on the bottom)? It would probably be only one type of sound that is muted. Also, have you checked the speaker volume wherever you have volume control to make sure it is turned up?

Have you checked that the sound cable connection [for audio CD's] from the CD-Drive to the motherboard hasn't come adrift. Perhaps you should try a different cable.
In the meantime you could connect your speakers to the headphone outlet socket.
Do you perhaps have two CD-Drives, only one of which has an audio connection, and your trying to play audio CD's on the one that isn't connected?
Every now and again I forget and do that.

I wonder if MP3's are played through the data cable connection and that's why THEY work?