Phone is stuck on Volume down?

[SA_128]

My Lumia 928 is currently stuck on volume down as if the button is pressed permanently. if I try to press the Volume up, it just goes back down to 0.

Sometimes the volume button works fine for a second, but then in goes back down to 0 and gets stuck there again.

When I try to restart the phone, sometimes it will show an exclamation point on the screen.

What should I do about this?

 

[crash0330]

I've had this happen to my old 1020. But I would just either turn it off or restarted and everything would get back to normal.
Never got the exclamation point. I would try restarting again, if you haven't done so.
Sorry if I wasn't much help.