Ex Vista machine now has XP, Cannot ping the network

Hi, I bought a new HP laptop which came with Vista home.I plugged it into the LAN. I tried join it to the domain, but it did not work. I enabled file and print sharing. I also tried switching off the firewall. It could not ping my Windows 2003 server or other machines, and vice versa. Yet I received an IP address from the DHCP server. I got so fed up, that I formatted the hard drive and installed windows XP, yet I have same problem. The strange thing is, if I connect through the wireless (Linksys) network, it works. But as soon as I connect the LAN cable, it does not. I cannot browse, or see other PC’s. Please help if you have any suggestions.