I Think reinstalling your sound driver will solve the problem.

this is going to make me sound really dumb.. but... whats that?

May be your sound driver file had been destroyed by virus. So u should installed sound driver file once again.

on my computer icon, right click and choose properties
then click on hardware and click device manager button.
on it uninstall your sound device under some sound icon.
restart and usually your windows will automatically detect the sound device, click cancel if you have the driver.
insert the driver cd an run the sound driver installer there.

fixed. just had to reinstall driver like you said. thank you very much.