Why can't I connect to the network?

I’m not sure why your co-worker can’t connect but even if it was a network issue, the network card should still recognize that it’s connected to something… meaning you should see the light on the network card. I would first check that laptop’s card is working correctly and then maybe check the cable being used to make sure it’s functional.

Was the co-worker using only wifi at home? It sounds like the drivers for the wired interface are installed because you got the “unplugged” error, but I would double check. Also, be sure to check the laptop’s network jack for bent, missing, or dirty pins ;-)

Along with @davidgro the co-worker could have been using wireless or wifi at home or elsewhere… or not at all but if so or if your office uses wifi maybe check that the wireless radio is turned on, or if the network card has a turn on switch or is installed correctly. Hope you solve it.