Volume does not work

This is really hard to explain, but whenever I try to turn my volume up, the pop up that usually comes up to show the volume increasing and decreasing is completely blank. So it just says "volume" and then under it, it's blank where the bar usually is that indicates volume increasing/decreasing....no matter what I do, nothing so far has worked. I hope somebody else has had this problem and knows what I'm talking about and can help me. Thank you.