This may be audio driver problem I had the same thing happen with Realtek Ac 97 drvier. I resolved the problem by doing the following.
Boot into safe mode - press F8 after turning on your computer after a few minutes your computer should be in safe mode. Go to Control Panel then Programs and Features remove audio driver then exit and reboot. Now download Vista compatible audio driver by going to Windows Update (in the Control Panel) if no driver is available from Microsoft try the vendor website most of audio and video drivers are available for Vista if your motherboard is fairly new (18 months or newer). When you boot into safe mode the video will appear different this is ok once you restart and boot into Windows Vista the video will return to normal. Hope this helps.

Raven