I have been having the same problem and it's driving me nuts, here's what I have tried (with no success):

WORKAROUND
- When the audio goes down, I go to the device manager, tell it to update drivers > Install from specific location > I will choose the driver to install. I select the option of Crystal WDM and then it copies the files and voila! the audio comes back, but only until I reboot or shutdown.

Also have tried:
- The installation program for the Dell audio drivers deletes the original Intel 82801 .INF files, so I made a copy of the files and restore them every now and then. The files are wdma_int .INF and .PNF
- Installing manually the Windows NT 4.0 audio drivers for the C610 and C640, which happen to have the same CS4205 audio chip. The NT 4 drivers are a non-starter with XP.
- I checked for IRQ and resource conflicts, but I couldn't find anything significant.
- I disconnected and reconnected the mini-PCI modem card, which can cause weirdness on some C-series laptops
- There are a couple of other posts in this forum that give a sequence to uninstall drivers manually, reboot, install DirectX9, reboot, install drivers, reboot, (or something like that) but that only works once, after a while, it goes back to "Device cannot start [code 10]"

TODAY'S FIND
I found somewhere the Realtek AC'97 drivers for XP. I don't know that these will work, but it's worth a try. I'll let you all know. AC'97 is yet another designation for the audio chipset of these laptops (why do they make it this difficult????)

Vince

I have tried the same as you but no success !

I tried that stupid DELL Diags and its all c.r.a.p, everything passed the test but there is no point to test the audio device.
If i go to the Mainboard i can test the stupid speaker with no success but its not the audio device.
There is also no modem device, yes i tried the diags with and without the modem and its always the same .
I also tried other testing tools and they all show me NO AUDIO.
This is not a XP problem its that stupid dell hardware.

I believe its that stupid bios update that makes all that problems, but there are no previous or the orginal bios updates to download from the stupid dell support.

Unbeleavable i contacted dell and that stupid idiots told me to read the FAQs and troubleshooting. That people cant spell the word PC and are working in the customer support.

Message Edited by centurio on 12-03-200607:12 PM