First thanks for the new versions. I still love to do things in Pagestream although I am currently doing much design work in Affinity after the organization I work for abandoned InDesign for cost reasons (Small Health care organization).

I opend a pagestream file and there was no text in it anymore. I tried it in PageStream5.1.2.x86 PageStream5.1.2.i64 and PageStream5.0.5.8 al with the same result. All pagestream files did the same. When I make a new file with a textbox and i type in it there are no letters apearing and the cursor stays at the same place

Sounds like you are running on Windows, and you need to add the system font path (C:\Windows\Fonts) in the PageStream File->System Prefs->Fonts dialog box.