Ubuntu – Virtualbox hangs when shutting down after having installed guest editions

The way to do this is to write a script to start your VM, wait until it terminates, and then issue the shut-down command.

Create a folder bin in your home folder (if it does not exist already).

Now create a file with the following contents. Let's call it win7vmshutdown, and save it in your bin folder.

#!/bin/bash

VBoxManage startvm 'Win7'                           # Start the VM.

sleep 10s                                           # Give it time to start up. 

while pgrep VirtualBox >/dev/null                   # As long as the VM is running...
do
        sleep 5s                                    # Wait a bit before trying again.
done

gnome-session-quit --power-off                      # Issue the command to shut down.

Make the script executable; enter the following in a Terminal.

chmod +x ~/bin/win7vmshutdown

In your Startup Applications, remove the VBoxManage ... command and replace it with win7vmshutdown.

The shutdown command will prompt you for shutdown; if you don't answer, it will shut down in 60 seconds. This gives you time to interrupt the shutdown in case of unexpected problems.

Reboot your computer to test.

You said:

Also, when virtual box starts up automatically, Ubuntu's desktop should not be visible.

To do that, you want to run your VM in full-screen. Install the Guest Additions in your VM, reboot it, and run it full-screen.

Unless you really need features only available with 4.3.20, I would suggest to use the guest additions from the Ubuntu repositories:

sudo apt-get install virtualbox-guest-dkms virtualbox-guest-utils

Restart your VM to apply the changes.