I've got the same problem.
It started with being unable to drop tokens from my mouse cursor. I then logged out thinking it was my browser, shut down Firefox, relaunched and logged back in. Now I'm stuck at the black loading screen, too.
There are no maps visible in the pull-down box, and no options to create a new one. I tried creating a new campaign, and it has the same problem as well.
Based on this, I suspect its a server crash on the back end. I hope nothing is permanently lost.
(Firefox 13.0.1, XP SP3)
Another thread was started with the same problems in the Help & Support forum: <a href="http://community.roll20.net/discussion/1758/cant-access-anything-related-to-campaign#Item_2" rel="nofollow">http://community.roll20.net/discussion/1758/cant-access-anything-related-to-campaign#Item_2</a>
EDIT @ 7:23 CDT: I just got back in. Lost about 15-20 minutes of gameplay, but otherwise its all there.
