|Is this another case of not keeping backup copies of your files? |
You might be able to retrieve them by installing recovery software, but for the best chance of that to be successful don't run any more applications or do anything which writes to the disk until after you've tried recovery software.
If you type file recovery software into Google search you should find some free ones.
Additionally (apart from remembering to keep backups in future) you should run Windows error-checker on drive C, or even better check it with the drive manufacturer's own diagnostic utility which is free. It will tell you if the disk is failing so you can fit a new one before it fails completely.