Can no longer select part of an equation

I can no longer select a part of an equation in Mathcad Prime 5 or 6..

With the cursor in an equation, pressing the space bar no longer selects an item in the equation. I used to be able to press the spacebar and select a variable. Repeated pressing of the spacebar extended the part of the equation being selected. Now pressing the spacebar with the cursor in an equation does nothing.

Pressing the left or right arrow key moves the cursor within the equation but pressing shift while using the arrow key does nothing. It used to select a portion of the equation.

Pressing shift while using the mouse to drag the cursor used to select a portion of the equation. Now it selects the whole equation.

I thought maybe my Mathcad 5.0 file was corrupted so I downloaded the trial version of Mathcad Prime 6.0 and have the same problem. BTW the trial version of 6.0 is useless. There is a big watermark diagonally across the page. It is so dark that in the confusion I can't see to enter enough into the sheet to evaluate it. I though this might be a Windows 10 bug but have no problems selecting, copying and pasting in any other applications.