Database Recovery


I had a 90MB Filemaker Pro 3.0v1 database (working in Classic Mac OS 9) mounted on the desktop of an iBook (Mac OS X version 10.3 - 800MHz PowerPC G3 - 128 MB memory). Last evening when I closed the database and shut down the computer, somehow the computer removed the database from the desktop and created a sparse image (thomasmacnish.sparseimage)in the FileVault. When I attempted to recover the database with the Disk Utility from the sparseimage file, the Disk Utilty reported that the sparseimage could not be repaired due to an "invalid b-tree node size."

My questions are:

1) Why did the computer remove my database?
2) Where did the computer move the database to?
3) How do I recover the database or the data in the database?
4) How do I prevent the computer from performing this action in future?

Thank you!!!