The default location on Windows is at: C:\Users\YOUR USER NAME HERE\AppData\Roaming\Microsoft\Templates\Normal.dotm
You can back this file up prior to making any changes. Another way, which is what I prefer, is to stay away from Normal.dotm, and make your own .dotm file. Especially if you ever plan to share your scripts/macros with others, as they may have already modified their Normal.dotm file.
If you like my suggestion, you can create a new, blank Word .docm file, or .dotm file. Add your modules and scripts to that, and keep this file in:
C:\Users\YOUR USER NAME HERE\AppData\Roaming\Microsoft\Word\STARTUP
It will be loaded whenever you start Word.
Note: Of course, this location depends on your preferences, where trusted folders are set.
Hope that helps! Sorry you lost your work. Maybe you have a backup of the Normal.dotm file in the folder above.