If all sound connections and controls check out, there's not much left to
look at. You could try reinstalling drivers. Or uninstalling the device and
drivers, then reinstalling (if it's a card, moving it over a slot sometimes
helps). Or try a different sound card.

sometimes I lose my sound for no apparent reason.. Everything is working
fine.. I reboot and the sound returns.. have you rebooted?  Rainy

Hi..   Have you gone through the trouble shooter in CONTROL PANEL to see if
it finds anything?  This could indeed be drivers but usually that doesn't
just happen.  It might be that your sound card has died.  If you can get into
device manager, does anything show up with an Yellow Exclamation point next
to it?  Is this a desktop or laptop?  New sound cards aren't that expensive.  
Might be easiest to replace it than to fight with it.