Hey, @Rodo2015. Welcome to the Photoshop Community. I'll help you figure this out. Before troubleshooting, ensure you have the latest version of Camera Raw installed from the Creative Cloud desktop app.
Where are the original NEF files stored, on an internal or external drive? In Photoshop, press & hold the CTRL + ALT key, go to Edit > Preferences > Camera Raw Preferences, and select 'Yes' when prompted to reset Camera Raw preferences.
Let me know how it goes. Thanks!
Sameer K
(Type '@' and type my name to mention me when you reply)