What distro/version are you using? That information usually helps get more specific help.
That message means that the VirtualBox kernel driver isn't running.
It's a shot in the dark, but you could try, as root, in a terminal,
to start the driver module.
Edit: If you try that and it doesn't work, post any error messages you receive in your follow-up, making sure to enclose them in "code" tags, which become available when you click "Go Advanced" down there at the bottom of the Quick Reply window.
