First of all its not slow, it has it pitch dropped which doesn't (or at least should) effect the speed, but it will sound odd.
Open the Realtek Sound Effect Manger - maybe in the sytem tray or also possible from the control panel.
Go to the "Sound Effect" tab and you'll see a something like:
I suspect from what you describe that the ? is showing as -1 or -2. Change it to ) or click Reset and you should be back to normal.