Fi PHP problem with my website

I've run into some difficulty while trying to make some changes to my website, not being PHP literate. Basically, I'm running an ecommerce site on Wordpress which has some PHP scripts in the theme and some plugins. I wanted to sort the products on my site by newest first, so I followed the instructions on a Community support forum and modified the WP E-Commerce PHP code...

In the plugin folder,

I exchanged this code

case "id":
$wpsc_query_vars["orderby"] = 'ID';
break;

for this
case "id":
$wpsc_query_vars["orderby"] = 'date';
$wpsc_query_vars["order"] = 'DESC';
break;

ad that's where my problems started. I have since been unable to log in to my wp-admin area. I get this error message :

Warning: Cannot modify header information – headers already sent by (output started at /homepages/46/d337328305/htdocs/mysite/wordpress/wp-content/plugins/wp-e-commerce/wpsc-core/wpsc-functions.php:1) in /homepages/46/d337328305/htdocs/mysite/wordpress/wp-includes/pluggable.php on line 934


I have so far updated my wp-ecommerce, returned back to default and the problem still persists. Now I have a problem with my slider on the front page and I need the site to be wholesome again.

So basically, what I need doing are :

1. Restore my slider and admin access
2. Sort products by newest display.

I need these done asap, and the first, most reasonably priced bidder gets the job.