Having suffered three hard drive crashes since July 2008 -- and two within the last month, the speed with which I get up and running again has begun to dazzle me :--)
Nevertheless, there always seem to be new glitches. Last time it was that my sound kept disappearing. Nope, it wasn't a missing driver. Wasn't even a corrupted or not-up-to-date driver. Intel (motherboard manufacturer) couldn't figure it out. Somehow, mysteriously, Windows Audio service kept getting disabled. So -- before you get beyond exasperation -- and when you are sure that your audio hardware is all there and not defective or broken, and you've downloaded, installed, and updated until you're blue in the face -- don't forget to check that your Windows Audio service is enabled and started. And make sure it’s set to Manual or Automatic on startup.
If you need instructions on how to do this: more later...***
Another audio issue: After installing a new video board -- yes, you read this right -- VIDEO board -- I lost the audio. Why? Some ATI boards (though it stands to reason that NVidia, and all boards with HDMI support probably can suffer the same fate) -- some ATI boards route the audio through the HDMI port, and so you lose onboard audio (i.e., audio from the motherboard). Vendor instructions tell you to disable your onboard audio. But, if you don't have an HDMI connection for your monitor, then obviously this cannot help you restore your sound. But, if you go into the BIOS and disable the new video board's audio, your problem should be solved. At least, mine was.
*** Instructions for enabling Windows Audio (or other services) in Windows XP
Go to My Computer (usually on Desktop or Start --> right side of start panel --> My Computer.
Right click on My Computer--> Manage (left click on Manage) --> Services and Applications (on right panel) (double click Services and Applications --> double-click Services
(make sure Services are sorted in Name order by clicking on "NAME" column. (Click once for ascending order; click again if it came up in descending order) Scroll down until you get to "Windows Audio" and double-click. Change startup type to "Automatic", and click on "Start" service if the option is enabled. You should now have sound!