Is your C: data store still viable?
Make a new backup on a new external drive.
Then, do it again. Always keep a second (or even a third) backup of critical files.
I have a home file server (of sorts). It’s an older computer that still functions OK, just not a hotrod anymore. It never sees the internet. That’s where I keep the working copy of my stuff (one of three copies). Another one I keep offsite at my brother’s house.
I learned the hard way...