This type of thing can happen if you accidentally drag a pane off the screen, or if you were using 2 monitors and drag a pane to the second monitor, then go down to only one screen (for example if you use a laptop with a second screen). I have seen this happen a lot with the Object Repository, but it can happen with other panes as well.
There are 2 ways you can recover the pane:
View>Reset Window Layout
Tools>Options>Restore Factory Defaults
Personally I prefer to to the View>Reset Window Layout because there may be other settings you've changed in UFT that you don't want to reset.