Many websites contain broken links. These are links that when clicked on either do nothing or go to a page not found error. These types of links often referred to as 404 or dead links can be very detrimental to a website and its performance. Not only are they viewed as bad in the eyes of the search engines such as Google, but they can also put off visitors to the site and make them leave before they have found what they were looking for.
It may be that when your site first goes live all the links are working as they should, but over time, if you are adding, removing or moving content/products/images etc. these links may stop working. There are many free programs that you can run on your site to find any broken links. Once you have these speak to your website programmer and decide if they need to be removed or redirected to somewhere else.