Internal website problems

We recently installed SBS 2003 R2 and had our internal website working fine but now we can’t connect to it. I used to type in the IP address, the welcome page would come up, and I could click on “My Company’s Internal Website” with no problems. Now when I click on “My Company’s Internal Website” I get nothing or “server not found”. This is happening internally on client workstations as well as the server.