My Vista Lenovo lost its audio entirely one day. Months later, I began the process to fix it. After much fussing around with drivers and the like, I saw the simple fix:
Go to control panel, hardware and sound, manage audio devices. There I saw the culprit message: "no audio output device installed".
Again, after much fussing, I realized that I could right click on that screen. There I would see a menu that offered to "show disabled devices" and "show disconnected devices". By tabbing those on, my audio drivers reappeared. I enabled them with right clicks and tested them immediately on that screen with a right click. All was well.
Simple fix. Nearly impossible to find.