I asked the same question and supplied the bug reports inside, in the link
I still need the answer, please help!
Hi aabun,
Duplicate report: https://answers.unrealengine.com/questions/150804/i-cant-launch-ue461-after-uninstall-reboot-reinsta.html
We will be closing this post in order to focus the discussion in one place. Technicians are assigned to your other post and are investigating the issue.
Thanks,
TJ