Windows 7 driver updating can be really annoying, when I arrived home my wife tells me we have an error message and the desk top has no aero and no sound. the message was that windows audio could not start. Yesterday I installed a sound card with a C Media chip Plus drivers - all was working well.
Looking at what has happened and I can see that windows update has downloaded more sound drivers, both Realtek and Uli for the onboard AC97 chip. No wonder windows audio could not start with three sound drivers installed.
After disabling the onboard sound in the bios I then could uninstall both the Realtek and Uli drivers to get the sound working again. Give me strength!
Could you post what Device Manager says you have for sound and what drivers you have installed.