The only thought that comes to mind here is that maybe at some point it was open on a second monitor and it's still trying to present there and you simply cannot see it?
If that's the case, try pressing and holding your Windows logo key on the keyboard, then press the left arrow key a couple of times and see if the window pops into the viewable area.
I tried that. No joy. I don't think it's running.
I checked my Task Manager. When I select and script and click Edit, Extendscript pops into the Task Manager list and immediately disappears.
I believe you can choose to install/uninstall Extendscript Toolkit separate from RoboHelp in the installer. A reinstall may be a little less work than you fear.