Can't create network connections

I have a dell dimension xps t600. I installed a D-link NIC and connected to router/internet fine. After 2 months it stopped working. I updated bios from A7 to A11 and installed a new hard drive and XP Home. I installed drivers for NIC but still could not connect to Internet - the computer is not being issued an IP address from router/dhcp (the router works fine). I manually configured an address and when I clicked OK on the IP properties page and then reopened the properties page, the checkbox next to “Obtain IP address automatically” was checked and the manually configured IP address was gone. I ran ipconfig and the static ip address displayed.
I installed a Linksys USB Wifi card. When I opened Network Connections, the Connection appeared as a Local Area Connection, not a wireless network connection. The same DHCP problem occurred.

I reformatted the drive and reinstalled XP. Same problem. I ran DellDiag and Checkit 7.0 on the computer and everything tested fine.

I installed a Linksys NIC. When XP detected the NIC, it showed up as an AMD something or other. I removed the Linksys card and installed it in another XP box and it was detected as a Linksys NIC.

I reset the BIOS NVRAM, but it did not resolve the problem. I am stumped. Does anyone have any suggestions? Anyone? Anyone?