The virtual window may have been placed outside of your video screen area. If you use multiple monitors this can happen. Right click on the application in the menu bar. Choose “Move” then try to use the arrow keys to bring the app window back into the screen area. If that does not work and if you have a way to use another system on the network to remote desktop into it, try doing that all applications open are mashed into the one screen. I used this method once to get a window that was “lost in space” back to where I could see it.