[Help] Unity 5 doesn't start

When opening a new project Unity opens a message box that says Hold On and it gets stuck on UnityEngine.UI.dll and never opens the project
I have made sure Windows is entirely updated.

System Info
Windows 8.1

Intel(R) Core™ i7-4500U CPU @ 1.8GHz 2.40GHz
64-bit operating system, x64 based processor

Graphics Card
Gforce GT 720M

So after trying EVERYTHING else I could think of, I refreshed Windows… And it worked. YAY. Now I have to reinstall every program I had on my computer, but it was worth it.

I have exactly the same error: uninstall and install Unity didn’t help. I can launch Unity 2017.x version though… but for plugins compatibility I do need Unity 5.x … anyone has a idea where to look at?