I'm an admin
in the "default" section permissions I set a read-only board except for the admins but why doesn't it let me create posts?
you must have a mod that broke something, admin always have all permissions unless something went horribly wrong. try to load clean files and test it again.
I put a virgin installation without mod I remember that the admin group like permsso had written "all" and instead there is the number 69 which is all the permissions I put on it
then that group is not the real admin group that is what is causing your issues.
how do i discover the real group from the level id? mine in phpmyadmin is the 18id level
It's group 1. If you deleted group 1, you broke your installation and no amount of fudging can fix that.
but can I change it from phpmyadmin? or should I re-install smf?
Fresh install in either a new database or a new database prefix. After that, don't touch the database directly!
I do hope you have at least one post count based group as well... very bad things can happen if you remove that.