Categories Page

[LBWeb]

I am trying to figure out which php page controls the main categories page. Problem when you click on the category in the left column it brings up the Categories page which is good, however the problem is I loose the menu and header across the top. Weird thing it only does it when you click on the category title and the rest of the pages are fine.

Any idea on which page needs to be tweaked to add in the menu.php command. The site is www.simply-sports.com.

Thanks for your help.