The blank screen problem sounds like a corrupted savegame file. The easiest way for most people to delete it is to completely delete Village Sim from their handheld using the Palm OS delete function. Even if you were to delete only the savegame file (using a file manager), you'd still have to enter the registration code again, since the registration info is stored in the savegame file. If you have a previous savegame file stored in your PalmOne folder on your PC (which might not have been corrupted), you could try restoring that file before you tried the more drastic measures.

LDW can also help with your registration code. Just fill out their support form with your purchase information and they will help you.