Can you show a screenshot of that particular icon, I can’t think of an icon that looks like a lock :)
Ah, that looks like one of the tool windows with zero size. Try making it bigger at the lower right corner. Then you can close it or drag it somewhere you want it to be placed.
Probably the output window, which gets automatically shown after a compile.
Edit: I need to make a window size sanity check, this zero sized windows are a pain.