Sigmatel audio problem... comes and goes

Have a DELL INSPIRON 1525 w/ SIGMATEL 9205 controller/STAC 92XXC -MAjor R180044 driver
AOAS (All of a sudden) after a windows update, audio quit working.

TROUBLESHOOTING DONE
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with VISTA32:

After doing a factory restore sound comes back (driver installed automaticaly). But on rebooting, the audio goes. sometimes it says "new hardware found" sometimes not even that.Reinstalling the driver has to be done only by manually running R180044.exe file (update driver doesnt accept the location of the file) but fails .(Exiterror:error=Device not present)

with XP
Tried formatting the disk with XP professional sp3 . XP doesnt automatically install the driver .Manually run the driver file.Audio works. After next boot audio fails.The CP>system>Device shows "audio device on Hi def audio" with a yellow failure mark.Tried reinstalling driver-fails with the error message.

Have upgraded the BIOS, Chipset...When I go to the BIOS with F2 key, the Onboard
devices list shows all the other devices except the Audio.

Can anyone help me pl. DELL says its the motherboard which needs replacement . I have my doubts ..why should it work with the factory restore if that be the case?
All the software used is licensed.

Thanks
Ashish