Very important Excel workbook opening blank and acting like a text file

My dad has a workbook that's very important where he keeps all his records that he has been updating monthly for 20+ years. Several years ago I did a macro that helps with the formatting and inserts a new column for the new month.

He told me it's not working and when I tried to open it I got a message saying "The file format and extension don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway?"

When I opened it there were no tabs and the whole sheet was blank. It gave me something that looks like you're important from a text file and asking how I wanted it delineated. No macros, no tabs, no data at all.

He is using Excel 2007. When I tried to open it on mine (Excel 2019) it gives me the same error message and when I get into it I get a message saying "Possible data loss. Some features might be lost if you save this workbook in a text (.txt) format. To preserve these features save in an Excel file format".

The original file is over 1MB. If I save it as a .XLS it is only 10kb.

What is going on? Since the file is over 1MB there's got to be data there. How do I restore it? I tried the "open and recover" button and it goes back to treating it like a text file.

Obviously I can't upload it here since it has sensitive info on it.

This may be moot, however it’s wirth asking: does your dad back up his data? If so, can you retrieve the last working version of the file from his backup?

Since xlsx files are really zipped xml files, I would be tempted to:
1) Make a copy of the file to do all this to -- just in case.
2) Rename the file to filename.zip
3) Unzip/extract the xml files.
4) Explore the various files and folders.

The most important thing I would be looking for is the raw data. If you can find the raw data among those xml files, then you can extract the text and enter it into a new Excel file.

I tried renaming it to a zip and then it doesn't extract.

On the plus side I managed to find a backup from earlier this month so he can easily restore everything. That was a real wakeup call to backup the file and keep multiple copies.

As you can imagine we were both panicking. I don't know what happened to his file. Maybe the power went out or something. I can't believe a file with so much data could just stop working.

I'm so glad I managed to find that backup!

I would still be curious if there is a way to restore the original file.

The bigger the file, the greater the potential for corruption. Glad you’ve found a more recent backup and glad you are going to implement a more rigorous back-up régime.

Administrative Note:

Please don't quote whole posts, especially when you are responding to the one immediately preceding your own - it's just clutter. It's OK to quote if you are responding to a post out of sequence, but limit quoted content to a few relevant lines that makes clear to whom and what you are responding. Thanks!

For normal conversational replies, try using the QUICK REPLY box below or the REPLY button instead of REPLY WITH QUOTE.

I tried renaming it to a zip and then it doesn't extract.

Curious. What is the original file type -- .xls (2003 and earlier Excel) or .xlsx (2007 and later)? Is it possible that something happened to incorrectly change the extension (it is really a 2003 and earlier .xls file, but the extension got changed to .xlsx or vice-versa)? That particular error warning is pretty common for me when I download spreadsheets from this forum. For some reason, a user here will upload a .xls file and, when i download it, it gets changed to .xlsx, and then I get the error. I have seen this error often enough in the context of downloading files from this forum, that I know to simply change the extension back to .xls and the file will open just fine. It seems like a long shot, but is it possible that the same thing has happened to your father's file? Someone changed the extension so that it no longer matches the actual file type and Excel cannot figure out how to open it with the mismatched extension?