If you run bcdedit with no arguments, you should see a property called hypervisorlaunchtype. This will be set to off or auto.
To disable Hyper-V in order to use VirtualBox, open a command prompt as administrator and run the command:
bcdedit /set hypervisorlaunchtype off
You’ll need to reboot, but then you’ll be all set to run VirtualBox. To turn Hyper-V back on, run:
bcdedit /set hypervisorlaunchtype auto