If you not have access to the php.ini file you can try to edit your htaccess file. (You find this file in the root of your Joomla! installation. If the name is htaccess.txt, remember to rename it to .htaccess .
Write this to your .htaccess file
Code
# supress php errorsphp_flagdisplay_startup_errors offphp_flag display_errors offphp_flag html_errors offphp_value docref_root 0php_value docref_ext 0