A few more questions...

What OS are you using? Is it different than what you have on the WORKING PC?
If it's Windows XP, try temporarily Disabling it's Built-In Firewall, AND the "UPnP" (Universal Plug-and-Play) Services...
What makes/models of NIC cards have you tried?
Have you tried the NIC card from the PC that DOES work?
(Personally, I prefer the 3Com 3C905-xx 10/100 series NICs, as ALL versions of Windows will NATIVELY Recognize them... No 3rd-Party Drivers needed).

-Tursiops_G.