I hid the menu bar in virtual box, how to show it again?
You can access the menu while the VM is running by Right Control + Home (by default). It will pop up as a contextual menu through which you will be able to reactivate the display of the menu.
Open virtual machine's settings, then User Interface page. Check this box:
Temporary removing of %USERPROFILE%/.VirtualBox folder with
mv %USERPROFILE%/.VirtualBox %USERPROFILE%/.VirtualBox_old
and starting a virtualbox from scratch allowed to solve the issue with the help of
hotkeys(Host+C & Host+Home, where Host=Right Ctrl)
from this tooltip