|Are all your client PC's getting their TCP/IP information from a DHCP server?|
Do you have a SOHO Router between the internet and your client PC's?
Open a command prompt window (Start >> Run >> type cmd and hit Enter) on the problem PC and on one that's working and type the following command:
Compare the output of both. The only thing that should be different is the actual IP address of each client PC. They should however be in the same subnet (example: 192.168.0.105 and 192.168.0.106). The rest (subnet mask, DNS, default gateway) should be identical.
If the above isn't true, post the output of both in here so we can see it.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.