If OE didn't open at all, I suggest replacing the DBX folders where they came from (which is why I didn't want you to close that folder). Return to that folder, right-click and select 'Paste'. (The folders should still be on your clipboard so you shouldn't need to copy them from the Store folder). You now need to check whether your Identity entry in the registry has been damaged. (See link below).
If OE opened, but failed to import one or more of the DBX files, you'll need to download the Macallan Outlook Express Extraction utility and extract individual e-mails. (See link below).
All of the foregoing text is based upon this web page:
http://www.insideoe.com/problems/errors.htm
I've simply tried to identify anything on that page which you might not understand, and re-word it. All that stuff about moving DBX files makes perfect sense to me. (i.e. I've often moved DBX files around and I know that, with care, it's perfectly safe to do so). Beyond that point, however, (i.e. when it comes to repairing registry entries or extracting mail using the Macallan utility) I probably don't know any more than you do. If you need to use the information towards the end of that page (i.e. the remedies suggested above don't work) I'll try to assist you with anything you don't understand but don't expect me to be an 'expert'!
Good luck ;-)
Chris