Sounds like that very old document might be your "blank document." In other
words, you might have inadvertently saved that document as your "normal
template" (Normal.dot).
Try:
Deleting all that content so that it's blank again
File > Save As...
got stright to the bottom of the dialog box, to Save As Type:
Select Document Template (.dot)
Select (and overwrite) the file Normal.dot.