I installed Windows 10 on a virtual machine, and everything is working fine. But when I go into fullscreen mode, the size doesn't change, and I get a black screen around the display. Some people suggested that I install the guest additions, so I did. I downloaded the file and inserted it. This did not change anything. I still get a black screen around the VM. How can I fix this?
Ubuntu – Black screen around Virtualbox VM in fullscreen mode (Guest additions installed)
The guest additions cd needs installed within the client. You can do this from the client toolbar. Devices -> Insert guest additions CD image...
That will mount the guest additions cd image. Click on it to run it. Let it install. It will then reboot the guest operating system. When the guest restarts and you log back in you will be able to go full screen and the resolution will adjust automatically. You can scale the window whatever way you want by dragging the corners of guest window and it will auto adjust to whatever that resolution is.