You notice that host names are no longer resolved to IP addresses?
The Time-to-Live (TTL) values for entries in the Hosts file are cached for one year. If you don't restart at least once during a year, the TTL values expire.
NOTE: Restarting the computer restarts the TTL clock.
NOTE: It is hard to imagine that normal maintenance and/or software updates don't require you to restart Windows 2000 at least once during a 1 year time period?