After installing Windows 8.1 on VirtualBox (as a virtual machine), my mousepad stopped working. It refuses to even respond. Currently, I am using a USB mouse. I have tried reinstalling packages xserver-xorg-input-mouse and xserver-xorg-input-evdev to see if that would solve my issue. So far, nothing has happened. I have never had this issue before with any Ubuntu version, or with Debian. I think it may have something to do with VirtualBox, but I am not sure.