It seems to me that the problem might be an IP addressing issue.
Do you know if in your actual network there is a DHCP server?
Normally, in home networks scenarios this is a service that is running in the broadband router.
The DHCP server i responsible to give IP addresses, DNS and gateway to local network clients. Without it you’ll need to manually assign all of these to your local computer(s).
So, if you are able, please check you router configuration if there is a DHCP server configured and running. It might be disabled or out of free addresses to lease to your last PC.
You might need further instructions to put everything right, but before instructing you anything else, we need some feedback from answering questions above.
–HE is correct better yet, check first your service provider for the information about the setting of your router they will walk you through that so it will be easier for you.Or i may suggest this site, this is where I get helpful tips about networking issues.