Thank you for trayin to help.
Solved,
- started PDF24 editor by icon on desktop
- taskbar sowed active application but no app scren
- Maximize vindow did the trick
- tried to close application as minimized trough taskbar icon, etc
- cant reoeat faulty condition
- it must be that win7 "rememberd" somthing what could not be "erased" even with reinstallation of application