What did you do when OE crashed A few months back? Did you basically start over with empty folders in OE? Besides the standard OE folders, did you have other OE folders you had created?
Have you ever changed the Store Folder location? That can be done via Tools, Options, Maintenance, and click on Store Folder.
630mb is large. I have more, but I've got thousands of messages, some going back a few years. Do you have a lot of messages with images/photos in them? Anyway, unless you have another/old Inbox.dbx file somewhere on your hard drive, you have indeed lost your old messages.
Try doing a search (right click on Windows Start button and select Search) and search My Computer for *.dbx.