Random crashing looking around through content/pressing Play

So pressing play crashes the editor now. It used to launch the test map in the window, of course

I just opened a TrueSky Sequence Asset. That has crashed the dev kit as well.

I am new to UE4/modding, is there a way I can revert everything to a new install?

Is it possible to break the editor? I’ve gone through a lot of cg software UIs and never had this kind of experience before.

I’ve already uninstalled/installed which hasn’t helped.

Any ideas?