While I was performing my recommended windows vista update, I followed instructions with restarting my computing. Once I turned my computer back on I noticed that I didn't have sound and my speakers aren't functioning. What do I do?

Reinstall the sound drivers for your machine.

I use windows update for criticals only. I might look in hardware updates to see what MS recommends, but in the past when I used them it only screwed me up so I do any sound drivers or video drivers from the manufacturers site only. Both the critical updates and the software updates are usually OK but anything to do with hardware avoid. For one, your supposed to uninstall previous versions before installing the new. Do you think MS does that for you? I have also seen drivers listed for hardware I do not even own. So watch out.

Use system restore to go back to when you did your updates. You'll have to redo them but avoid any hardware updates this time. If system restore fails from within windows try doing it from safe mode. Just reinstalling your sound drivers may leave the wrong ones that screwed you up still there and cause conflicts.