Ok .. I'll have a stab. When you say you've made stuff 'invisible', do you mean you've used the Visible option in the toolbar Object > Properties window, or have you gone into the Material room and turned Transparency up to 1? If the former, are you 'raytracing' the render? If you are, have you removed the 'Visible in Raytracing' option in the Object > Properties window? How about the 'Remove Backfacing Polys' in the Render Settings window?

Sorry for all the questions instead of a direct answer, but I think raven is right and your camera's view is obscured by a wall. It'll show in a render but not in Preview, depending on the combination of options you're using. A way to check would be to try a render using the P4 settings (in Render Settings). If that shows your character ok, but raytracing doesn't, then that'll just about prove it.