Internet Connection Problems

Hello,
I recently set up a Windows Vista computer, and am trying to connect it to the internet, using normal cables.
When I am on the desk right next to my router, and I plug the cables in, Windows detects the network and I can access the internet as normal. However, when I am on the other side of the house, I cannot use the internet, and Vista does not detect the network, however my old computer does not experience this same problem when used in the same place.
Thanks