Try using System Restore to get the Registry back to a time before the problem first occurred. In XP, go to
Start>All Programs>Accessories>System Tools>System Restore
and tick 'Restore my computer to an earlier time'.
Go to Start/Run and type "services.msc" then hit the 'Enter' key (or click 'ok'). The Services window will appear. Scroll down until you find "Windows Audio" towards the bottom of the list. Check that it is enabled, set to automatic, and running. If it isn't, double click on it and change the Startup type to Automatic, then click Start, Apply, and OK.
To check for defective hardware on the motherboard, run Dell Diagnostics interactive audio test. To run Diagnostics restart the computer and as soon as it starts to boot up hold down f12. Select 'Diagnostic' from the boot menu. The computer will run its pre-boot assessment tests for 3 or 4 minutes before the Dell Diagnostic starts. These pre-boot tests play some beeps and tones through the system speaker but this doesn't test the rest of the audio hardware adequately, so you still need to let Dell Diagnostics run after the pre-boot tests finish.
When Dell Diagnostics opens, select 'custom', then the audio test. This will test your audio system independently of Windows and drivers, meaning it doesn't matter if they are working correctly or not. Alternate between using headphones and listening to speakers in case only one is working.
[If you have ever reformatted your hard drive then the Diagnostics partition might have been wiped off.]
Dell Diagnostics will play some audio and ask you whether you heard it. If you answer 'no' then the test generates an error code that means you indicated you did not hear the sounds it played, but it doesn't pinpoint the exact component that has gone bad.
If you do hear the audio that means the hardware is okay but there is a problem with the software or configuration.
Jim, thanks for the help, but no luck. My system restore doesn't go back far enough. Like I said it is my sons laptop and this happened a while back and I just got it to fix. Windows Audio was on and set to automatic, so that wasn't it.
Still hoping someone will come up with an idea.