I wrote this page in hopes of helping others facing something akin to this perplexing situation I encountered myself on a Dell Latitude D600:
One day, the audio on my Dell D600 laptop running Windows XP just suddenly cut out. I tried to fix it for a while, and then it suddenly started working again, right after the system told me it had found a new modem and installed a driver for it. I didn't really understand what had happened at the time, and just considered it a fluke.
About six months later, the audio again stopped working, out of the blue. This time, though, a lot of working on it just would not fix the problem. The symptoms were as follows:
1) No audio, just the system beep from the built-in speaker
2) A yellow exclamation point on my audio device in the Device Manager, with the properties tab telling me that the device "cannot start." (In my specific case, SigmaTel C-Major Audio STAC 9750 AC97, running from STAC97.drv et. al., but I'm guessing this could happen with almost any audio device.)
3) No amount of audio driver un-installing, re-installing, updating, or what have you was able to fix the problem. Old versions, new versions, rollbacks, system restores...same symptomology, error code 10: This device cannot start
4) Fancy restores of system files, flashing the BIOS to the latest version, updated CODECs, re-installing Windows Media Player, taking all the SigmaTel keys out of the registry, what have you, always the same symptoms.
5) Testing the sound card itself with diagnostics, which boots independently and loads its own drivers, showed that the device was working - the diagnostics could make beautiful music, record, and playback. So this was not a hardware problem...I thought.
After much consternation, I remembered the earlier episode. I looked for the modem in the device manager...not there. I tried testing it with diagnostics...it did not show up (as if it were not installed). I swore the thing had a modem, even though I never used it. I kept coming back to this, finally concluding that the modem was the reason my sound card would not start. Then I got adventurous, opening up the laptop (following the directions in the service manual - don't try to guess these things open!!!) all the way down to the modem, pulling it out, blowing all the dust from its neighborhood, and firmly-reseating it. I reassembled the laptop, turned it back on...and viola, the annoying Windows startup sound was beloved to behold for perhaps the first time ever.
This turned out to be a hardware problem, but with the modem. I guess the modem needs special access to the audio card in order to let you hear what's going on on the phone line or something. So if you have made a diligent effort to fix error 10 (cannot start) on an audio device, to no avail...here's one more thing to try. It worked for me, and I don't think I'd ever have stumbled onto it based only on what Windows was telling me.
One more thing:
Opening up a laptop is not for the brutish or faint of heart. It's easy to break stuff. Don't make this the first thing you try! Try reinstralling drivers and doing all the other things you can read about on other pages first. If that doesn't work, look for your modem in the device manager. If it is missing, look for it with diagnostics. If it is missing or not working, consider trying to re-seat the modem, with the understanding that there are a lot of small screws, you'll need the right tools (a good #0 Phillips scredriver, at minimum), some experience not losing bits and organizing them as they are removed, and great care such that you don't break all the flimsy plastic bits that allow a laptop to remain light. Before I did this I replaced the hard disk and added memory to this laptop. Those were both easier and less dicey than the modem re-seating business. Take your hard disk out first and set it aside carefully. Better still, back it up completely before you even take it out. Good luck.