tl;dr: PlayClaw 3 (gamecapturing software) stops UE4 from Launching.
I thought I’d throw in my 2 cents at the recent problem:
I’ve been having problems opening UE4 as the launcher suddenly stopped working. The launcher would not open - it would load for a few seconds sometimes bring up the splash screen but then just close itself down. I’ve searched for different solutions, but I seem to have all the needed items. As a last resort before reinstalling windows I remembered that PlayClaw had previously interefered with games that would not launch so I closed it down and tried again: Bingo.
I’m currently downloading the Engine again as I had deleted it to reinstall it - it seems the problem is fixed and unless you hear more from me assume it is! 