Server 2000 is not very smart. It could be that it doesn't know the old cards are gone, and it will not allow you to use the same IP on the new NIC. Then again it could be lots of things. DNS would also be a likely cause. Can you try it with only one NIC installed that will help you narrow down the issue.
Not to sound like a jerk, but Windows 2000 is way, way past its' sell-by-date. Bad idea to keep running it. Window 8.1 running as a pseudo-server is much better than Win2000.