Ok, well the drive wasnt actually empty unless somehting purposefully overwrites the disk. I think if it was looking into a little futher you could have been able to save your information (if it was important if not its a waste of effort).
However, I clearly have no idea how good your friend is with computers so I really dont kwow where to begin. It could be that the kid never installed your sound drivers onto the coputer again. The first thing I would do is - well it depends - Do you have a Dell or a custom PC (and by Dell i mean any brand).
If you have a brand name computer than you can go tot heir website, go to the support section, and find all the drivers and software from your computer model.
Otherwise (or both ways actually) I would go to windows update page manually not the automatic download thing) and click on "custom" NOT EXPRESS. Then allow it to do its scan and see if there are any windows updates.
NOTE: only the critical updates are automatically checked off, you have to manually select the reccomended updates and one of the sections will be for drivers / hardware updates. Download whatever drivers it think syou dont have and see if that solves the problem.
(Short answer)
right click my computer and goto proporties (haha i said goto) then click on the hardware tab and click the device manager. Once this is open search the list for sound devices, or sound card or somehting and click the plus sign next to it. Does anythign appear there? if so tell us. If not, looks for anyplace that has yellow exclimation points next to it (this means that there is a problem) and tell us if you see anything with the yellow, esp if it said sound card heh.
