hm... looks like you did something wrong. i don't know what you did but maybe you should try to do one thing after another and not all faces at once.

...
to start over either select all faces ([a]), press "u" and select "reset 1/1".

or set the lower window to be a button window, press [f9] to show the edit buttons and then in the mesh panel press the texface [delete] button. i think this also deletes the texture assignments though.