You start the command (OPEN, LAYER, BHATCH etc.) and nothing happens: LT acts like the command is running, but you have nothing on screen. You are able to cancel the command.
Your pop-up may be off screen: start themmand, on the keyboard use the combination of ALT+SpaceBar+M then use the arrow keys on your keyboard to nudge it back to view (this is a Windows feaure, you can use it to recover any lost pop-up in LT or other programs).
You can also change the resolution of your monitor to lower settings, the layer manager will show, move it to be centered, then change resolution back.