If I load any scenario which is missing the 'DVINITIALIZED' line in the EMS entries, then switch to the main control panel with F1, my monitor goes black... even if Orbiter is just running in a window.
I'm guessing this is a combination of an Nvidia DirectX bug with something weird that the EMS is doing when that variable isn't set in the scenario. Either way, the default configuration of the EMS should be checked to ensure that it's in a sensible state if the scenario doesn't contain this line.
This happens, for example, with the standard historical scenarios in CVS. Add EMS_BEGIN, DVINITISALIZED 1 and EMS_END, and it stops.