Elitebook Notebook Screen Display Dims When Mouse/Cursor Is Not Moving

[CDobyns]

Have an Elitebook 840 Notebook which developed an odd problem with the display recently.   The screen display dims, whenever the mouse/cursor is not moving.  When it is moving the screen display rises to the regular brightness level.  Changing the brightness setting on the Display properties has absolutely zero effect on the screen display as does using the Fn keyboard functions.  The thing that seems to affect the screen display, is if the cursor is moving.  Pressing the keyboard keys has no effect, and the screen display will also intermittently go completely black for a few seconds.

So, some of the things we can eliminate from consideration are (I've checked all of these): 

-Any changes to the Display brightness settings

- Any changes to the Power Management or Group Policy settings

- Any updates to the display screen device driver

- Anything have to do with the Adaptive Display settings

- Conducted a full virus scan, but nothing else seems to be affected/malfunctioning

- Even tried a full operating system restore, while keeping all applications and files

I'm willing (and capable) of trying out various suggestions (exclusive of any of the ones listed above).   This seems to be somehow a hardware issue (although the screen will display full/normal screen brightness, if the cursor is moving - so the display itself seems not to be the problem and is otherwise working normally), and not a configuration/software setting issue.  Given that the input from the mouse/cursor (movement) evidently changes the screen brightness I wonder whether there is a problem with the mouse/keyboard.  This key board is relatively new, but it might be worth it to just de-installing and re-installing the keyboard/connections - to see if that does something, since that's about a 10 minute job.  Other suggestions?