WP User permission issue

I installed a WordPress for a client last year and everything was OK. Now i tried to add a new plugin but i see that the button is missing. If i try to add plugin-install.php in the link i get this message: You do not have sufficient permissions to access this page. Also i see that there are other features missing like: Appearance -> Edit theme files.

So i followed the next steps without no result.

1. Disabled all the plugins.


2. Replace all files except wp-content folder with the original WordPress files.


3. I changed the database version so that i get the part with wordpress update database.


4. I changed the theme with a default WordPress theme.

In the table wp_usermeta row wp_capabilities i see that i have a:1:{s:13:"administrator";b:1;}. I changed this to a:1:{s:13:"administrator";s:1:"1";} but nothing happens.

So what could be the problem and how can i fix this ?