Hi,
That's Program Editor
5 ! The simulation window should (re-) appear when you select Simulate / Run.
It might have been moved very nearly off the edge of the screen. Or you could try: (Menu Bar) > Simulate > Simulation Panels > Reset Default Panel Positions.
But maybe MS has done a Windows "Upgrade" as my PE5 suddenly seems to be loading/running extremely slowly.
Cheers, Alan.