Lost Password
Fragment of a discussion from Project:Support desk
Why did you ever think changing the DB schema would be a good idea?
Firstly I would be reverting back to a backup to when people were able to login then I would follow one of the guides on Manual:Resetting passwords where the maintenance script option is probably the best bet for you, or if you are running at least 1.18.0 (can be checked at Special:Version on your wiki) you can use the built in Special:ResetPassword page as pointed out by wargo.
As for enabling the option to create accounts, Have a look at Manual:Preventing access although that won't help at all if you have DB issues preventing people to login at all.
