I think you should use FM Pro Forum instead of Report an issue for that kind of problems. But anyways :
• Try the File menu command "Open Recent File" when FileMaker is open.
• Check for a backup of your databases.
• Note that you can perform find on your desktop or your server based on the .fmp12 extension on both Mac and PC Operating system. Thus, you will receive more results and have more chance to find your lost file.
• If you find your file BUT you cannot open it because damaged, you can try the FileMaker Recover function. More info here : http://www.filemaker.com/help/html/recover.39.10.html#1029844
PS : If you want follow this thread, please create a new one on FM Forum tab on the top. Then, clic "New forum post".