Sounds like a bad Driver, Remove old Drivers and install the new one.
You Could remove restart and do a windows update and it should see that it is missing and download the new one or go to the motherboards website and download the new Driver yourself but make sure you do not just install it over the old Driver also are you using any other Sound Driver as that can give you this Problem as in the Video Card Sound Driver, What did you last update that is a easy way to find the problem.