develop the habit of saving more than 1 version of your project, like project_01 project_02 etc...
I always follow this workflow ...
is your project file size 0 ?
try this on a copy of the damaged project file, which is usually used to change to previous versions, but maybe it will work:
zip the project file in 7zip, right click on the project and select extract here under 7zip, then open that file with a text editor. You'll see a bunch of text, but look for <Project ObjectID="1" ClassID="62ad66dd-0dcd-42da-a660-6d8fbde94876" Version="xx">
Change the version number to 1 and save the file. Then right click the file again and select add to archive under 7zip. Change the format type to gzip and change the file name to whatever you want with the extension .prproj.
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