Since this morning the editor fails to start.
and if i try to run from VS:
not just the C++ projects. the whole editor crashes at start.I decided to uninstall and download it again - lets hope that fixes it.
Is it a project with C++ code? I messed one of mine once and it would crash right at the start. I had to solve the bug in my code in order for it to launch the editor.
Good luck! 
Well uninstalling the whole thing seems to solve the problem. I still have no idea what corrupted the DLL, but I guess the problem (for me) is resolved for now.