DT crashing, says Inbox.dtBase2 still open

Just now, for the first time I tried saving as a PDF to a DT database from the Print dialogue in Preview and since then DT has gone haywire.

I now keep getting dialogue boxes warning me that Inbox.dtBase2 is already in use and it opens previously closed databases. The database (I use several) I’d like to open says it wasn’t closed properly last time and when I press Continue and either Restore Windows or Don’t Restore Windows it immediately crashes the program. Can anyone advise? I’ve saved the database as a copy but that’s also corrupted. I’m worried that I’ve lost over a GB worth of PDFs.

I’ve also tried restarting the computer, etc. Any advice? A little bit desperate and worried here that everything’s gone.