Can I change user permissions using my SQL database? No user login on my site

The user login block disappeared from mysite.com. Have been through the forums and tried
everything, still access denied for all pages.

Is there a way to change the anonymous user permissions from the SQL database?
I am a newbie and don't know how to work with SQL much. I see the user table and the permissions table.
I tried running the following query but it said it was redundant.

INSERT INTO node_access VALUES (0, 0, 'all', 1, 0, 0);

Just want to get the login block back so I change everything the correct way.