One of our employees is trying to access a specific website. That website won't load on any computer inside our network, but I can tell from outside the network there's nothing wrong with the website. If I change the DNS on the client PC to point to a public DNS such as 220.127.116.11 instead of my internal DNS server, the website loads fine. I'm sure this means there is a problem with my internal DNS server, but what is it, and how do I find/fix it?
The website in question had previously been working fine, and I'm unaware of any changes made.