It could be the database, I would recommend re-installing phpBB. First I would do a backup of everything on your forum if needed:
http://php.about.com/od/phpbb/qt/backup_phpbb.htm
That tutorial is a bit outdated, but it should still work. If this problem has been going on since installation, you probably wont need a backup because there probably isn't anything really sensitive on your forum. Next would be an uninstall of phpBB.
If you installed via fantastico or installatron (I'm not sure if x10 offers this), then you can use the un-install link in those modules. Otherwise you can just delete everything under the forum directory from your account via FTP or the file manager. Then you can delete the mySQL database.
Just go to the mySQL databases module in cPanel, and delete the database and the database user.
Be careful! Make sure no other things installed on your account use the same database. If you've only installed phpBB you're good to go. After the database is deleted, you can start with a fresh install of phpBB, and then restore your backup if needed.
If you've got any questions on clarifying any of the above, I'd be happy to help. You can post here or PM.
Also other users may have some better ideas bellow...