So I'm still not 100% what the issue is. Do you have the account email and password and can you log in on PC?
If you can, just make a new user on the PS3 and try use the details you have to log into PSN. You can worry about the old local users trophies and saves later.
Another thing is, if you have multiple local users on your console, make sure you have not already linked your PSN to a different local user, it will not let you link 2 local users on the same console to the same PSN account.
Before messing around too much, It might be a good idea to make a back up of your dev_hdd0/home/ folder and your dev_flash2/etc/xregistry.sys file. This can be used to restore the console accounts to its current state on the off chance you do anything destructive like delete a user by mistake.