From another user:
"Me and friend had this problem once.
To sum it up, Windows Update on Windows 7 was stuck trying to install .NET Framework, which was preventing Steam or UE4 from installing .NET Framework.
We uninstalled the game, disable windows update, installed .NET Framework manually, then reinstalled the game.
Later we required some odd files from a vc++ redistribution package, but I guess this could of been caused by the bad installation."
Please let us know the result, GTO