The volume up and volume down keys on my keyboard don't adjust the volume but mute it instead.

[ScaryPMA]

I have a Lenovo ThinkPad 13. I have already tried reinstalling the keyboard driver which doesn't get rid of the Problem. All of the other keys work just fine and it isn't that big of a problem as I can still adjust the volume via the volume mixer but it's frustrating nonetheless.
Any help is appreciated.

 

[hang-the-9]

Could simply be physically broken