Since you seem to have no idea what else on your network has that IP, try this:
a) if 192.168.0.4 answers pings, try unplugging other devices on your network until the ping responses stop.
b)
http://nmap.org/dist/nmap-5.10BETA2-setup.exe (sorry for direct-linking to an executable; you can use the
download page but it's not the best-organized webpage in the world)
run zenmap, type 192.168.0.4 into the targets box, and see what it says... particularly the OS details, seen 2/3 of the way down in this screenshot:
Echoing gigabuist's comments, I would urge you to track it down, rather than ignoring it. It's unusual for one computer on a local network to trip the windows firewall of another computer without human direction. Since you haven't enumerated what else is on the same home network, and explicitly ruled those devices out, there may be unmaintained computers, or embedded devices, that may have been hacked.
(as you may have gathered, whois is not a good way to find out where an IP is physically located. It gives information about the person or organization that registered the ip, but does not give information about where that IP is routed. There are geoip databases for that purpose. for instance,
http://www.maxmind.com/ http://www.geoiptool.com/ )
