You only get blocked if you use the wrong password too many times.
In Revolution, if you edit the DB, you'll have to clear the cache to be unblocked. That means deleting the files in the core/cache directory.
If you don't have a core directory, it's MODX Evolution and there you can just edit this file rather than changing the DB and clearing the cache:
assets/cache/sitecache.idx.php
Change
to
and save the file.
Once you're in the Manager, you'll have to edit your user to unblock yourself before loggin out.
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PLEASE, PLEASE specify the version of MODX you are using . . . PLEASE!
MODx info for everyone:
http://bobsguides.com/MODx.html