I have installed VirtualBox on my computer and am trying to install ubuntu 12.10 on the virtual machine. I went through the installation process, and didn't get any error messages. When I start the virtual machine, it brings to an ubuntu log-in screen, and I enter the password I selected. Then it takes me to a desktop screen, but without any icons or anything on the screen. I tried to install Guest Additions, but it tells me it can't mount the CD/DVD graphic and asks if I would like to force mounting.