Mixer device not available - services.msc doesnt help

Hi,

Im having this problem with the Realtek AC97 crad on my Gigabyte M57SLI-S4 M/B. Im not able to access the mixer device despite the drivers being installed correctly and the hardward installed and recognised. I know this is a common problem that is usually attributed to the Windows Audio service being stopped but that doesnt help me here. The service is set to automatic and has always started but still i get nothing. tried ASIO4all drivers but to no avail.

What is really weird is that when windows (XP Pro) boots the startup jingle is clearly playing, and the volume control icon appears in the system tray briefly but after a few seconds then disappears, upon which i have no sound. This seems to have first started happening when i updated the NVIDIA PhysX drivers. I dont know why this would affect anything but it seemed too much of a coincidence. Anyway, anything i do regarding the PhysX drivers doesnt make a difference. Please help!!  

Win XP Pro
2GB RAM
Gigabyte m57SLI-S4 M/B (with Realtek AC97)
AMD Phenom X4
640MB Gigabyte 8800GTS graphics

Thanks,
James