Conditional Formatting Manager Screen just became too small

Conditional Formatting Manager Screen has been working and appearing correctly up until today.  When I click on Conditional Formatting icon and scroll down to "Manage Rules", after I click on it, only half of the screen appears.  I am not able to resize.  Please see attached pic.  I cannot get to the part of the screen that allows what cells the conditional formatting can be chosen.  

Any suggestions will be more than helpful.