I have a dell optiplex 360 desktop pc that does not connect to the network(LAN).
What happens is when I connect ethrtnet cable on then port it does not show that its connected to the network on the lower right corner of the monitor also the LEDs on it's port donot blink as it normally happened before, but when i connect a different computer on the same ethernet cable it connects to the network without giving me a hard time.
Is the NIC on its own expansion card or part of the motherboard? If its on its own card, maybe the card needs to be re-seated. If its part if the motherboard, you should boot into the BIOS setuo and verify that the NIC is not disabled.