Apart from the game itself, all other executables crash on launch

[Romulator]

If the core game is running fine, then the editors should be good too. If it's your first run (at least, to completion), give the editors some time. Their first load should be quite lengthy to install a bunch of stuff.

If you're running Steam, do an Integrity Check. If you're missing any files from the editor/viewer folders, this will fix them.

If nothing seems to work, run the level editor till it crashes, close it, then post the LevelEditor.log file. It can be found in Documents/HPL3/