are you connecting through a lan? if so make sure on the internet options/connections tab that you go through the setup and choose local area network. also on the lan settings unless you are using a proxy server you need to make sure all those boxes are unchecked. if none of that fixes the problem check your tcp/ip properties on one of your other computers and verify each and every setting on the computer that will not work. if that still doesnt fix the problem run winipcfg and see if you have an ip address, if you cant get an ip address your network card is probably bad.
***of course some parts of this only apply if you are on a lan***