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Hope this isnt your security site that you got locked out of... thats never good for business.
Well if you have made a backup of your site recently then you can simply overwrite... assuming that you havent done that though.
so heres what you do.
dump, fresh install.
make a back up of your user tables pretty regulary.
I make an immediate backup upon install. that way if i get locked out i can just pop up the original prfx_users.sql and be on my way. I would rather lose users that can always be re-added than have to do the whole site all over again.
good luck. hope someone has a better way :(