As jademan wrote, see: Corrupt or Otherwise Broken Audacity Project Recovery
How is that connected to the computer?
Working on Audacity projects on external drives is not recommended. Sometimes it will work OK, but other times you can get database corruption, which is quite likely what has happened to your project. It’s fine to move a project to an external drive, even a network drive, once Audacity has been closed, but highly recommended to move it back to a local drive before opening again.