As a fellow musician I feel your pain.
Possible problems can include: (from most to least likely)
1. Corrupted drivers that haven't been removed properly and may need to be removed manually.
2. Corrupt HWmanager (may be reading the file wrong or the wrong file.)
3. Corrupt windows.
4. Fried onboard sound.
I would go through and eliminate the first three by running the troubleshooters and diagnostics and by checking your driver folders for any straggler sound driver files. OR/AND go to dell's site and ask tech support or download their model specific drivers.
What driver were you running originally?
EDIT: I found this oldgrumpy had a good how to with suggestions I suggest reading if you haven't