The default groups which should never be deleted (i dont think its even possible to delete them) are the first 5. Which are titled as follows:
Group 1 - Administrators
Group 2 - GlobalModerators
Group 3 - Moderators
Group 4 - Users
Group 5 - Guests
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You could try the following route, but without knowing which main account groups you've changed / deleted, all I can offer is a guess in to where to begin troubleshooting. Especially since you haven't mentioned about having a backup to compare with.
Assuming that your account number is "2", and your table prefix begins with "ubbt_", manually or from with your phpMyAdmin, update your account USER_MEMBERSHIP_LEVEL to "Administrator"
UPDATE ubb_forum.ubbt_USERS
SET USER_MEMBERSHIP_LEVEL = "Administrator"
WHERE USER_ID = "2"
