Thank you for the detailed description. can you please elaborate on the whirr? Is it a long, high-pitched whirr, a low, shorter type whirr, or an unusual, sounds-like-it's-broken type whirr. Just kidding. Most of the time people only give the bare minimum in terms of what is happening, so your information is actually very helpful. I'm assuming that you are using Excel, but if not let me know and I will adjust my suggestions.
It sounds like Excel is assuming that the spreadsheet includes a lot of area that it doesn't including blank cells, leaving your real work out in the middle of a field of blank paper.
This could be due to some formatting change or any change really, that Excel mishandled. If the spreadsheet is not complicated with links to many other spreadsheets, then you can first try creating a new worksheet, copying the cells from the existing spreadsheet and then pasting it in the new one. That way, if there is a an erronious character in cell c:10000 for example, it will not longer be there.
If this would break the spreadsheet, or if you find this easier, this is another option:
Also, does it appear correctly if you do a print preview?