I would like to know how to unfreeze the F6 volume button on an HP windows 8.1. I pressed it to mute the volume and now it is stuck with zero volume and a black rectangular box in the upper left hand corner of my screen. I can not undo it. Today I turned it on and the black box is back ... if anyone can help I would appreciate it. I tried clicking the FN button and the F6 button together and did not fix it.