If your browser has the auto-complete feature turned on, you may be able to click on the blank user name box and get a list of entries you have made into this and other user name boxes. Possibly you might recognize the name if you saw it.
Otherwise, you'll probably have to create a new character AND also write to GuessWHO (http://www.bulfleet.org/viewtopic.php?t=13116), who is an admin, and explain what happen so they don't think you have multiple accounts.
Your old account will automatically be deleted anyway after 25 days of inactivity.