Windows 8 comes with Hyper-V pre-installed. If you want to run Virtual Box, you must completely uninstall Hyper-V through the “Add and Remove Programs” option from the Control Panel. Failing doing so will result in:
- Virtual Box will display error messages when starting up your Virtual Machine
- You will not be able to change the number of processors in Virtual Box
- You virtual machine will run very slowly because of the inability to increase the number of processors
- Hardware acceleration will be disabled
Stopping the Hyper-V service is not enough.