No Connectivity Issue With Vostro System

My dad bought a Vostro 220 and had it shipped to me so I could set it up for him.  His AV software (BitDefender AntiVirus 2010) didn't install correctly and caused the computer to hang up when it attempted to load itself during the boot routine.  The software was difficult to uninstall, but after repeated bootings into safe mode, I was eventually able to uninstall it.  Unfortunately, "something" happened to the network card driver or configuration during the uninstall process, and I have lost all network connectivity.

The lights on the router port the system is connected to are lit as they should be, the link integrity light on the Ethernet port on the computer is lit as it should be, but in the Network and Sharing Center, there is no network connection indicated.  I tried to Diagnose and Repair, but according to Windows Network Diagnostics:

"Windows tried a repair but a problem still exists. The network adapter is not correctly configured to use the IP protocol.  Make sure your Internet Protocol Bindings are correct.  Ensure that Internet Protocol Version 4 (TCP/IPv4) and Internet Protocol Version 6 (TCP/IPv6) are selected in the configuration for the network adapter."

Boxes for both TCP versions are checked.

I have checked DHCP settings in my router's configuration, and all is as it should be.

I have checked Device Manager, but there is no indication that the device is malfunctioning.

After performing the following actions, the problem persists:

Reset the router and the modem.  (Another computer connected to the router via Ethernet has full network connectivity, as do all wireless devices that connect through the router.)

Updated the driver with a more recent version from the driver downloads for the system on the Dell site.

Disabled and reenabled the NIC in Device Manager.

Uninstalled and reinstalled the driver.

Disabled the device, deleted the driver, replaced the driver from the Dell Drivers and Utilities disc included with the system. 

Reinstalled the OS.

The system is running Vista Home Basic, and the NIC is integrated (Realtek RTL8168C(P)/8111C(P) Family PCI-E Gigabit Ethernet NIC (NDIS 6.0)).

Sorry for the long post.  I have absolutely no clue what to do next short of contacting Dell's Tech Support, and imagine their solution will be to replace the motherboard (although I could be wrong, it seems to me not to be a matter of catastrophic hardware failure).  Does anyone have suggestions how I might proceed to fix the problem?  Thanks very much for all responses!