How to backup Complete Current Database:
Copy these items from this folder "C:\Program Files (x86)\AllMyMovies":
<Name of your DB>.amm (Database)
<Name of your DB>_images (Folder)
Trailers (Folder - IF any)
If you are able to access your registry
Also, if you want to keep your current configuration (Image size, display, etc.), Manually export these two registry keys to save AllMyMovies total preferences:
Note: I periodically make a backup of my DB from inside of AMM, and store it on a flash drive just in case I am faced with this same issue.