Fictional car model "Borchia V8 VC" - about to call this finished

I was just about to change the lighting and render out some new ones but the scene won’t load at all now. I haven’t
opened, moved, changed or deleted anything since I last opened the editor and captured the shots in the post above.
I’m out of ideas on what’s happened here.

It’s all built into the Advanced Lighting starter content level. I double click it in the Content browser but it won’t do
anything. Right clicking pops up an error message “Failed to load assets” but the Message log doesn’t list any errors.
“Map check complete: 0 error(s), 0 warning(s), took 57,767ms to complete”. That is all it says.

Does anyone have any ideas what might have caused this and what could I try to make it open correctly again?
UE4 version is 4.8.3 which is the same one I had earlier.