Update Centos to version 7.6
Centos is regularly updated - when the number after the . (dot) is updated is it a minor update. But still minor updates brings new and fresh software in the latest releases.
Centos 7.6 is not compatible with VirtualBox 5.2.22.
Update VirtualBox to version 6.something and then update your Centos.
If you accedentially updated your Centos first the it can be a bit problematic to install the VirtualBox extension because the mouns doesn't work in the mix of Viirtualbox 5.2.22 drivers and Centos 7.6 drivers.
Follow these instructions and you should be up running soon:
1. Update VirtualBox to version 6.something
2. Start your Centos - hope that yakuake starts automatically.
In VirtualBox menu click on Devices and select Optical Drives. In this menu select Force unmount if it is available.
3. Open yakuake and execute
] $ sudo mkdir -p /mnt/cd ] $ sudo mount -t iso9660 /dev/sr0 /mnt/cd ] $ sudo init 6
after the reboot your mouse may be working again and the window resizes to its maximum.