Sorry for the slow reply on this.
Sounds like your best bet would be delete PlecoDict completely and reinstall. For the flashcards, if they weren't lost when your motherboard was replaced there are two different places they might be:
1) In your Palm Desktop backup folder. Go to My Computer, C, Program Files, Palm (or palmOne or Palm Desktop), and there should be a folder inside of that with your username on it. Open that folder, open the Backup folder inside of it and check to see if there's a "PlecoDict Flashcards" file in there. If there is, move it (and the "PlecoDict User DB" file, if there's one of those) out of that folder before continuing.
2) On your Treo. To back these up, download and install the free utility FileZ from
http://www.nosleep.net. Open it, tap on the View and Edit Files button, then on the little triangle next to Internal. Scroll down to PlecoDict Flashcards, select it, scroll to PlecoDict User DB C-E, select it as well, then use the menu "Copy" command to copy these two files to your Treo's memory card.
Once you've done both of those things, you can safely delete PlecoDict from your Treo (using the Delete menu command in the application launcher screen) and then reinstall it.