why does the brightness indicator keep appearing on my screen?

Yesterday the volume indicator kept appearing on my screen, set to mute. Pulling up the settings for volume and turning the mute off didn't work - it reverted to 'mute' setting.

Today it's the brightness indicator which keeps appearing at the lower center of the screen. No way to modify it or get it to disappear. I've re-started, updated software and then restarted, shut down and restarted but the indicator keeps showing up.

I found one tip that plugging the keyboard into a USB extension might help and it did, for all of five minutes. Now we are back to normal: the brightness indicator is onscreen, set to max brightness, and it will not go away. Using the settings to modify the brightness doesn't work: if I reduce the brightness it resets itself to maximum brightness.

Help!