If a file is too big (i.e. accidentally created file of maximum size, so you can't delete unnecessary empty columns/rows) how are you enabled to add in additional rows of new information? I can't find the right words to access Excel help on this.
Hard to diagnose and treat without a more complete description of what you did to create file of max size, what those supposedly empty cells contain. You might be able to highlight a lot of the existing rows and columns--the ones you don't really need--and use "Edit...Clear....All"