1. System Restore to when it worked.
2. Use "Driver Rollback" on the audio and NEVER EVER accept a driver from Windows Update.
3. It is possible for the audio system to fail and never work again. In those cases we use the usual sub 9 buck USB audio since fixing is as much as a new laptop.
4. After the owner backs up their stuff, use the Recovery Media. If the sound fails you know it's hardware.