Missing IP?

[antispam@demon.com]

The IP address hasn't changed, ip 146.83.240.200 is telling you that it can't
reach that host.  That is the last system in the route to get to 200.1.28.20.

> In the last two days I have been getting probed by an IP 200.1.28.20. When I
> try to ping the address I get a message:
> 
> Reply from 146.83.240.200: Destination net unreachable.
> I will assume that the computer with the IP I am trying is off. But since the
> IP has been changed to 146.83.240.200. How do I find out how this is.