Did you use the RealTek drivers
from the motherboard vendor? If not, give them a try as usually the motherboard (or PC) vendor's drivers work best (and in some cases the only ones that will work).
You could also try a System Restore using a restore date that is before your problem and whatever you changed, as that MAY fix your problem.
If neither of the above work, just try uninstalling/reinstalling the RealTek in the Device Manager. In the Device Manager, RIGHT click on the entry for the RealTek and then LEFT click "Uninstall". DO NOT check the box to also uninstall the drivers. Restart the PC and when Windows starts it will detect and reinstall the RealTek. If there were a Windows sound corruption this usually fixes it.