Sorry for the late answer, but try the following:
Start the engine from the “UE4Editor.exe” directly.
To do that, go to the engine folder, the default installation path should be something like “Program Files\Epic Games\UE_version”, and you’ll find the executable under “Engine\Binaries\Win64”.
While you’re there, check that you have the “Engine\Source” folder and that the code is there. If it’s not there, try reinstalling the engine entirely.
Otherwise, you can also try using the source engine from the github repository instead of the launcher one.