I’ve run into a bug with VirtualBox and at least Windows XP where trying to reboot or shutdown the VM causes the shutdown process to hang at the screen displaying: Windows is shutting down. This problem has to do with mouse pointer integration.
To fix the problem:
- Start the VM
- Machine > Disable Mouse Integration
- Machine > Close > Save the machine state
- Start the VM
At this point shutting down or restarting the VM should not hang. Thanks to this post for pointing me in the right direction.