Computer won't go online

 We have cable with a  Belkin router and I know the cable works because I tried my laptop and it works fine. We have 3 computers, one for the mother in law, my kids bedroom and my main one in the dining room. The one thing I noticed is that their ADDRESS TYPE is ASSIGNED by DHCP and the one that does not work says AUTOMATIC PRIVATE ADDRESS, it is  STUCK at that type. It also has a different address, the 2 computers and my laptop addresses is as follow, 192.168.2.60 (this is where the router and modem is connected), 192.168.2.14 (my kids) and 192.168.2.68 (laptop). They all have the same number in the SUBNET MASK ( 255.255.255.0) and DEFAULT GATEWAY (192.168.2.1). The one that is not working has and IP ADDRESS of 169.254.163.15 (The last 8 numbers change everytime I reboot) and SUBNET MASK ( 255.255.0.0) and NO NUMBER on the DEFAULT GATEWAY, it is also STUCK at those numbers. I talked to network "experts" already and still won't work. We ping numbers and still won't go online. I even put the the IP address myself and it won't work. I ran DIAGNOSTICS and  REINSTALL WINDOWS XP and still won't go online. I even bought a NEW NETWORK CARD and no help. The LAN window says I am connected and able to send and receive packets of information. It iI have exhausted all my little computer software knowledge that I have. I just bought this refurbished computer just 6 months ago, should I just send it back?  Any help would be greatly appreciated
Thanks