DNS not Updating

I am having some DNS issues with my server. I have a OS X Serve running 10.4.6 and I am using it as a DNS server. NIC is set to 10.1.5.2. My company recently changed it's website and in doing so changed hosts as well. So now it has a new IP address. Although no one from in our building can get to the new website even after 5 days now.

When I change my laptop from my DNS server(10.1.5.2) to google's 8.8.8.8 I can get to the website just fine. Then, when I change my DNS back again and ping the domain url it is sending packages to the old ip address and not the new one.

Either my DNS server is not updating, telling people to look for the new ip address or it is statically set inside the DNS server. I have no idea how to fix this without changing 150 plus laptops from my DNS server to google's. But that is not the solution. There has to be a way to change it internally. Any assistance would be great. Thanks