Just had another client puzzled by this issue, their IT provider couldn’t figure out what was wrong either. The application (in this instance ACT!) appeared to start, but wasn’t visible. Ultimately, the window was off screen. They had used an external monitor and had been using the app on that second screen. They’d shutdown, removed the external monitor, now the app was not ‘there’ even tho it was in the windows task bar.
The solution? ALT-Space | Down Arrow | Enter | use the arrow keys to reposition the window onto the current active screen. Or use this utility: Sheepdog to do it for you.