Strange broken links? HELP please

Hi you can see my site at https://www.sonsurf.co.za/shop

You will notice that everything seems to be working fine, except for when you click on the categories in the black area at the top and also once you want to add something to your cart and click "add to cart" or "checkout" it does the same - comes up with a blank page??

I have found the items are going into the cart, but it just comes up black when you click most of the links.
Very strange??

Would really like some help.
Thanks

Looks like you're yet another "victim" of template monster.

This forum is full of horror stories about the Monster!

It also appears that your problem occurs when you have only ONE product in a category.

You can try adjusting the Layout Settings in Configuration for skipping one-product categories. (I have NO IDEA if this will help).

Try adding more than ONE product to your categories. This may provide a temporary "fix".

thanks.
It still isnt working, and its mainly the "add to cart" button and single products in a category that dont work, youre right.

Any other thoughts, otherwise would it maybe work if i were to change themes?

Right I added a error log file and it came out with this error:
[25-Mar-2008 14:09:09] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/sonsurfc/public_html/shop/includes/languages/english.php:1401) in /home/sonsurfc/public_html/shop/includes/init_includes/init_templates.php on line 78

Now im not sure how to fix this, but its clearly the problem...

Never mind im talking to myself here, sorry everyone!
Found the problem.
So in future if anyone else has the same issue, go here:
https://www.zen-cart.com/tutorials/index.php?article=87