I found this was a problem for previous versions of windows, but the fixes for them won't work for Windows 8.
(like right click on the program in toolbar and moving, also cascading didn't work for me either)
SO! In case ANYONE runs into this problem, i'm going to share my fix in hopes it saves some poor soul the frustration.
Problem: A program isn't showing up on either monitors. It's running, you just can't recall it. (WINDOWS 8)
I did this through Catalyst Control Center, but I don't see why it wouldn't just work through Screen Resolution.
1. Rearrange your monitors (in CCC or Screen Res.)
3. Grab it and bring it back to your main display.
4. Switch your monitors back in the correct order.