i Had the same problem my fix Was
you have to go to the admin back panel and enable "error reporting" to "Maximum", but since you can't access the back panel, here is how to enable it
1) Go to your site root directory
2) find the file that is named "configuration.php"
3) Open it with any text editor (notepad)
4) Find the line that says "var $error_reporting = '-1';"
*Here, the Joomla default is -1 if you have not touched this setting at all.
5) What you need to do is change "-1" to "6143", so it would look like this:
var $error_reporting = '6143';
if you still can see errors try this
put the following code at the END of the configuration.php file BEFORE the closing ?>
ini_set( 'display_errors', true ); error_reporting( E_ALL );
which there i had problems with the 2 component plugins jd downloads and Hit Sniffer Live Stats
so i unistalled them both and delete all connected plugins and mods from phpmyadmin db
Problems solved for me hope this helps out a bit guys and thanks to the guys on forums like this that help and have progress me from noobe to amatuer lol god bless you all
Important::: someone said rename configuration.php dont!!! and yes you can use configuration.php from another site just need to change
public $dbprefix = 'to what your DB prefix is here';
public $secret = 'to what your secret was here is here';