2 days ago I worked on a spreadsheet when I think a Windows update was loaded. The file was previously about 100 KB, and it is now 120 MB and totally unusable. Any ideas what might have happened and how I can go back to Saturday when life was so simple?

Sure don't know how to go back to a time when life was simpler, but one thing you can try is by saving the file as a .xlsb.

Depending on how much info is in the file, might it be worth it to start over?

Thanks jeffreybrown. I can't do much with the file as it won't even open, presumably as it is so large. I use it daily to log data and as I have found an earlier version I could revert to that, but that would mean losing about 10 days of data. Consequently I thought if I could open the big file in another application, such as notepad, I might be able to copy the missing data and then just delete the big file, but Notepad can't do this and I don't think a suitable app exists. Would I just be able to change the extension on the file name to .xlsb?

Try deleting all rows after the last actual row. The rows will reappear but if there was anything in there, perhaps not visible, it will bloat your file size. Do the same thing for columns.

edit: Since you can't open, this won't help.

Thanks gebobs. I did manage to open the file today, (it took about 30 minutes), but it just froze when I tried to delete whatever may have been lurking in "blank" rows and columns. I had to close it down, but opened it again and was then able to copy all the data I needed into a new spreadsheet which is less than 1000th the size of the original, which I have deleted. I still have no idea what went wrong but thankful it's been sorted out.

That's a relief, eh?