You need to get someone who knows about computers to open your computer and check to see what kind of sound card it has. Then type the model number into google, followed by the word driver, and look for a download.
Also download and install Belarc Adviser
and run it and find your motherboard model number. Then google that followed by the word drivers, and look for the Chipset Driver (essential) and audio, LAN, and wireless (eg broadcom, atheros, intel pro etc) drivers too.
You could also try going to Control Panel > System > Device Manager and looking in the list for the sound device. It will have a yellow exclamation mark next to it. Then double click it and then click the driver tab in the window that pops up. See if you can update it from there.
Whenever you wipe a system and do a clean install, this is what you have to do to get the new operating system to 'recognise' what the various parts of the motherboard and sound cards etc. At some point you'll have to find out what kind of graphics card you have too, and download and install drivers for that, they'll probably be ATI or nVidia.
Hope this helps
ps Don't let your son at your computer again! :)