First, Linda should check if the problem is at the computer or at the switch. She should try to connect one of the non-working computers to a wall jack. If the computer communicates with the network, then the problem is: the switch, the cable connecting the switch to the wall jack, or the wall jack the switch is using.
So, next she should connect the switch to a jack that is 100% working. If it is ok, than the problem is the jack or the cable. She should replace the cable with new one. If it is OK, then the problem is the jack.