[Chimera-users] Question Regarding on Finding Distances

Hi there, My name is Padua and I'm an undergraduate research assistant working on pharmacogenomics. To do this, I have been using your program UCSF Chimera. I've been trying to find the distances between a protein and a drug but keep running into problems with selecting an atom in the graphics. When I try doing Ctrl-click or Shift-Ctrl-click to select an atom, I don't select anything at all (nothing is highlighted green as its supposed to when something is selected). My professor I'm working under has tried changing the mouse settings as well. Is there something I'm missing that's not listed in the User's Guide and tutorials? Much thanks, Padua