It's impossible to say as we are unable to see your site. However when I try to access http://www.valucopy.com/index.php I get a file not found message which suggests that you don't have Zen Cart installed where you think you do, and certainly not where your URL is pointing.
You must have it installed somewhere, as you can get to it via the admin, but I'm guessing that this is because your configuration files point to where it is actually installed.
Another possibility is that the permissions on the index.php file don't allow any public access so that visitors can only access your site when referred from another page on the server.
You will probably need to talk to your web host to sort this out.
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