Unity won?t load any Projects!

My Unity will start to the Project Windows, but when i choose a Project, a short loading screen will appear and disappear in a second. And nothing else will happen.
If i start from beginning, it will say “youre project has already been loaded”…
All i can do is killing it from the Taskmanager.

Reinstall Unity wont help, and i have no clue what to google, since i got no Error Message.
Is anyone Familiar with this Problem and knows what to do?
Thx a lot in advance…

I’ve had this problem before and I this thread helped me:

The UnityLockFile was the issue in my case.