audio driver drops out

I have been having a problem with my audio driver. It is a Sigma Tel C
Major on my Dell Latitude 800 Laptop. I have a Windows XP professional OS.

Recently, the audio driver seems to disappear when I close my system down.
I reinstall it, it plays fine and then disappears again after I close my
computer down an then reboot.

Does anyone have any suggestions as to what might be causing this type of
problem and a permanent fix for it.

Thanks,

Richard