If you have the issue where your website is showing up everywhere except for your local network, check out the info below.  The issue is your server was once setup to either host e-mail, like exchange, or your website.  Now it is not hosting your website and you need to point your local DNS to the new IP address of the web server hosting your website. 

To test this theory, you can easily change the HOSTS file in a computer on the network to point to the IP address of the web host.  
How to change the host file:

To fix the issue network-wide, you have to change the DNS in the Domain Controller to point the domain to the actual external IP address of the webhost.  

How To:

Go to the server that handles your DNS

Open DNS manager

Expand the server, Expand the Forward Lookup Zones

Make sure that you have a zone called: yourdomain.com

if not, create it

Expand the zone

Check to verify that you have two records;  An A record without anything and an A record with www.  
The A record without anything will work for http://yourdomain.com
The A record with the www will work for http://www.yourdomain.com
Both of these records should point to your web hosts IP address

*note, you do not have to check the box to create a reverse lookup as you do not host it on a local machine.

Propagate the changes to other DNS if they exist and you are done.

To be on the safe side, right-click the server and select Clear Cache.

Then the clients need to run "ipconfig /flushdns" in cmd line

I would do it in the servers too to check.