The window is probably opening off screen. Try this: Open the Add More Imagery window, even if you don’t see it. Hold down Alt, and tap the space bar. Release Alt, and tap the M key. Tap any arrow key. Now move your cursor, and see if the add location window is attached. Left-click to drop the window off where you want it to be located. What version of SketchUp are you using? Are you still using SU2017 as indicated in your profile?