This is a shot in the dark but becouse you have not UV maped yet.. the UV's might be to jumbled for the UV texture editer to handel them.. I would try selecting all the faces on your model and do a plainer maping on them. makeing sure "make a new uv set" is not ticked. and Thin trying to open your UV editor.

it might help. its just a gess at what is cousing the problem though.

still looking for anser to first question..