I got this message when I tried to get on today.

The cd key that you installed with has been disabled. Please contact blizzard entertainment technical support for further assistance.

I haven't used any hacks or anything so I don't know why I would have been banned.

If this was a first offense on the Cd-Key, it will be usable in one month
You can also try emailing blizzard technical support about this issue.

You can contact the "Blizzard" technical support and politely ask them why your CD key was banned.

does it give a code ?

You can call the blizzard hot-line and they will explain why.