I would look at a driver issue here,, just because you reformatted does not necessarily mean that the nic is working correctly,,
find out what your onboard nic is,, go to the manufacture site and look for current drivers that coincide with the nic,, or,, if you bought a system from IBM, Dell, etc,, look on their site for the driver matrix for your machine,,
you could try to ping the nic , go to dos prompt and type :
ping 127.0.0.1,, this is a loop back and should give you an idea of whether the card is functioning,,
check the pins where the ethernet plugs in,, any bent? straighten them,,
If you have another NIC,, disable the onboard and install a different one, if that works, then you can say something is wrong with the NIC,,
After you find out the issue,, (I am sure you will),, what is the warranty on the MOBO, machine,, ??
see if you are covered,, get it fixed,,, if not,, a New Nic is about 20 bucks,,
cheers,