Why not see if you can do a system restore to a point before you installed VBox.
If there is anything in the registry that is causing the problem this will fix it.
I would have to reinstall Windows 7 from scratch. I installed Virtual Box as probably the first application - even before installing Office and other software.
XP VM is working fine on my laptop. I am going to install Virtual Box on my laptop and see what happens. My laptop has very little software on it and it would not be an issue to reinstall Windows 7 on it.