New computer on network (windows 2003) won't connect to the internet

I have added a new computer (lets call it LD) to the work network (windows 2003) and it is the 9th computer on this network. Problem I'm having is that once it's connected I can see / access the network but it will not connect to the internet via LAN, however, I can connect via wifi. Now this is where it gets tricky...If I turn off 1 particular computer on the network (lets call it AB) - I can then get the LD computer to connect to the internet via LAN but then when I boot AB back up it is now connected to the network but has no Internet accessibility.

Things I have tried:

1. Reset the modem and router

2. Called our ISP and had them send a refresh signal

3. Moved the plugs on the switch to make sure one hadn't gone bad

4. Checked to make sure both computers are set to automatically obtain IP

Please help

via Bleeping Computer Last 20 Posts http://www.bleepingcomputer.com/forums/t/511866/new-computer-on-network-windows-2003-wont-connect-to-the-internet/