Hi there!

Had my 8000 pro for four days. Worked properly til now. Charged phone overnight. After that it shuts of every time i push the power button. If i just wait for the screen time out to go on i can just unlock it with the fingerprint sensor and it works just fine. But as soon as i push power button it shuts the phone down.

Faulty power button maybe?

Please perform a factory reset and report back if it solves your issue.

Done hard reset. Makes no difference. Everything else works. But when i press power button to switch off screen the shut off/restart etc menu comes up and after a few seconds the phone restarts. Acts just as if the power button is held down.

It definitely looks like a faulty power button. Please contact your seller to have your phone replaced/repaired under warranty.