DNS server stops responding

The DNS server is setup on a Windows 2000 Server machine. The network card went bad a couple weeks ago, so I had it replaced with a Netgear PCI 10/100 card. I’ve been noticing that after x amount of time (around 5-8 hours) the server stops responding to incoming and outgoing connection requests. All pings to the server are timed out, and the activity monitor for the network connection shows no activity (even though it is still enabled). When I disabled and reenabled the connection, everything started working again, web browsing, etc. Any ideas on what the problem could be?