sound problems on 1501 laptop

Hello-

I recently have lost all sounds except the on board beep. Media Player 11 gives an error code " Windows Media Player cannot play the file because there is a problem with your sound device. There might not be a sound device installed on your computer, it might be in use by another program, or it might not be functioning properly.". Other players give similar error codes. The device manager shows the legacy, audio and SigmaTel hi-def codecs installed and functioning properly. When I try the volume control or sound recorder, an error message "sound device not installed, go to control panel..."

I tried system restore 3 or 4 times and it indicated a successful restoration each time. The first 2 times I tried it, the audio came back, but then stopped working again, but other earlier restore points had no effect. I believe the problems started when I installed TVersity, so I unistalled that, reinstalled the SigmaTel audio hi-def codecs, but had no effect. I've also tried uninstalling, then reinstalling the chipset and processor drivers which also had no effect.

Specs: Dell Inspiron 1501, Windows XP SP2, Media Center 2002 edition, AMD Turion X2 TL-50 processor, 2G RAM, ATI 1150 video card, AVG 7.5 anti-virus, ThreatFire anti-spyware.  

Thank you-

Stan Anderson