@Ragnar1989 that's strange. Does it throw any error?
Try to download the tool from this link then. If it still won't launch, right click on the exe and run it as administrator. Another option is to try and launch the exe from CMD. Reloading the PC might also be worth a try, I guess.
The pic you linked doesn't show up but based on your description it seems that you're dragging the pak file to the tool exe? If that's what you're doing, it won't work unfortunately because the tool requires the path to the game folder and the path to the Granny Viewer exe.
Here's a brief video to give you an idea on how it's supposed to work.