I have a server running Windows Server 2008 R2 hosting a DNS server, exchange 2010 and is a domain controller. One computer on the network (and domain) can ping the server 25% of the time, also when I try to ping it's own hostname it also does not work. However another computer that is on the domain can ping it fine, and another computer on the network but not domain can ping fine as well.

The computer that cannot ping the server is setup to use the DNS server running on the server only (secondary dns points to nothing) and it will resolve the hostname of the server to the external IP not internal when the other two computers correctly resolve the internal

All 3 computers and server are connected directly into the same switch. Does anyone have any ideas on how to fix this? Thanks