I'm having a problem with my machine. A site that I used to be able to access is no longer being found. After running nslookup, I notice that about 9 times out of 10 it returns a specific IP which times out if I ping it, but about 1 in 10 times it returns a different IP which works when I ping it.

I've even tried adding an option parameter into nslookup to hit different DNS servers (such as Google's public DNS) and am getting the same result.

Any idea what would cause the IP returned by DNS lookup to change back and forth like that?