If this can help, I recently had problems with sounds not working at all on the Internet. To solve it I had to import a file to my Registry(regedit) to solve the problem. Dunno if that when the sound stop being loud but might have something to do with it.
I think if there's a way to literally reset my Sound settings to default it would help. I already tried from Control Panel--> Sound but nothing works. Maybe a reg?
This is my sound at max,as you can see it barely goes to 50%. (OS : Win7 x64)


















