Cannot create new project or open existing project with Unity 5.2.1f

Unity Editor
1

Hey everyone!

I have encountered a very strange problem with Unity 5.2.1f Personal Edition.

When I try to create a new project or open an existing project, the Unity Editor doesn’t show up and the Unity Thread goes to an inactive state. It seems to stop at UnityEngine.UI.dll. After that, I have to stop Unity via the Task Manager.
If I turn of the Internet connection, the Unity Editor does show up when opening an existing project, but freezes before loading completely.

Version 5.2.1f has worked before, but stopped working suddenly.

I tried reinstalling Unity and restarting the computer multiple times.
One time I got an error with the error code 1400 after installation, but I could not reproduce this message.

The log seems normal except the last lines:
Error Log

Reloading assemblies after successful script compilation.
Begin MonoManager ReloadAssembly
Shutting down Remote Indexer

Task failed: Downloader Task

OS: Windows 8.1 x64 with latest updates installed

On my second system with Windows 7 everything works fine.

Does anyone know how to solve that problem?

l.g.

2

I have just found out, that the Unity.exe file doesn’t display the normal Unity-symbol in the explorer.
file-size: 52454KB (53 712 344 Bytes)

May that file be corrupted?

If so, why doesn’t a reinstall of the program fix this issue and where can I download the non-corrupted .exe file?

An answer would be very much appreciated.

l.g.