But you can still see the blocks and other things? Because when it happened to me there was absolutely nothing -- I was floating in a black void consisting of collision data only.
Wherever you have your background in, lets say ModelData[1], right-click that, mouse over "New>" and the click "Character animation" -- you should now have a "AnmChr(NW4R)" or something there. Go to your background in the Advanced Model Editor -- what you need to do now is give each of its bones keyframes (making all the boxes with numbers on the right tab turn yellow).
In the model previewer, select the new animation in the modeldata the model is in (right tab). Select each bone (left tab) and then hit the copy then paste buttons shown below:
This is needed because the scale and rotation of the models are changed from their t-stance, and thus need keyframes for the game to recognize.
That was from my thread with the same issue.
And thanks.