you may need to re-install the drivers for your sound device. If you don't know what it is, you could run an "Aida32" scan which will identify it for you, then go to the maker's website & download the drivers.
ah, sorry.
google "aida32", download & run the utility - it will identify the principal components of your pc.
if you hover the cursor over the description of your sound device, you should get a hyperlink to "download driver".
download driver for your device, then install.
in the aida box, click computer > summary, then scroll down to "multimedia", next to the audio adaptor line will be the description of your audio device. If it's in blue, hovering over it will bring up the "driver download" box. If it's in black, make a note of it, then google the device description - this should take you to the maker's website, then go to the drivers page.
I have had exactly the same problem. After advice I looked for a disc for the motherboard which originaly came with the computer. With luck I found it, it contained the drivers for the audio devices. Happy hunting.