Have you tried 'device manager'? if you can't find what you're looking for - right-click - 'scan for hardware changes', if ther'es any audio drivers missing it'll find out for you and ask if you want to update. Also check in - control panel - admin' tools - services - make sure 'windows audio' is running and on 'automatic'. the only other thing i can think of, when you were installing HDD you may have knocked the souncard or your audio lead, if it's ever so slightly out of whack it may not function. try pushing your soundcard in further and check any cables. Also check the speaker icon in your taskbar and make sure nothing is muted and check you have correct speaker settings.
If you've checked all this already, sorry to go through it all again. It's just what usually what goes wrong when audio is out.