1. Check that the file is saved to the correct folder or directory.
2. Check to see if there have been any changes to the desktop environment.
3. Restart the computer.
4. Check if the saved file is compatible with the version of PowerPoint.
5. Check if other files saved to the same folder have disappeared.
6. Check if the document is corrupted.

If none of the above solutions help, it is recommended to contact IT Support.