How did you design your report? What view are you in? (List, table or Form?)
Sub summary parts?
If so, have you sorted your records in the order required for the sub summary parts to be visible?
If you've been working with your data on another layout that lists the same table occurrence in "show records from" in Layout setup... the actions you've taken there may have changed the sort order to something that hides the sub summary parts. If you don't have a body or if the fields in the body touch or cross the boundary between the body and the nearest sub summary part, this may be enough to produce your blank layout.
Ah - I think the sorting issue might be it. I've just resorted it in the correct order and it's all working now. Thanks!