The first thing to try is an upgrade install. Run Setup again with the Upgrade box selected.
If you still can’t log in, you’ll have to modify the MODx database directly:
Log into PhpMyAdmin through cPanel. Select the DB, then the modx_user_group_roles table, then the Browse tab.
Make sure the Super User authority level is 0. Change it if not (by clicking on the little pencil in that row, changing the authority and clicking on the upper "go" button).
If it was already at 0, browse the modx_access_policies table and see what the ID of the Administrator policy is (probably 2). Write it down.
Browse the mod_access_context table and wherever the ’principal’ is 1 (that’s you), change the ’policy’ to the Administrator policy (2?) using the method you used above.
There should be an entry for you for both the ’mgr’ and ’web’ contexts. If they’re not both there, stop there and let us know, otherwise, do the next step.
Delete all the files in the core/cache directory (be careful not to delete the /core directory itself!).
Then try to log in again.
If none of that works, we’ll try some other stuff.