Unity Editor is not displayed

For some reason when I start Unity. I choose a project and than nothing happens, I can see in process monitor that Unity Editor process is running and I can’t open the same project again with this Warning that it is already running but no Unity Editor is displayed and I am not able to work in it at all.

No Unity thing on taskbar, no UI, nothing. Anybody has a suggestion or and idea why it behaves like that?

Somehow it works now. I havent changed anything so I have no idea what fixed it. Will monitor a bit longer and than possibly close this question.