Hi there
Thanks for fast reply. I did another test: creating a new machine it just showed me 32-bit versions available - what?? So I configured a Linux Ubuntu 32bit one and started it with the image. I got the message "Raw-mode is unavailable courtesy of Hyper-V" - ok, so some more HyperV stuff is still active as you mentioned. I searched for and found that one I CANNOT POST URLS

Solution:
STEP 1:
Open the command prompt as an Administrator.
STEP 2:
Run the command with no argument: bcdedit
After you run the above command, you will see that the property hypervisorlaunchtype is set Auto by default.
STEP 3:
Disable Hyper-V by running the command: bcdedit /set hypervisorlaunchtype off
STEP 4:
Restart your PC system to use VirtualBox.
With me the auto launch type was still on auto, I deactivated, rebootet et voila - VirtualBox is running fine again, also offers me to create 64-bit versions again
Best
Udo