When the initial theory is not confirmed, a technician should reestablish a new theory or escalate. In this scenario, testing the port on the switch is a logical next step because it helps in isolating the problem further without necessarily escalating yet. Upgrading firmware is generally not a targeted next step when dealing with basic connectivity issues. Changing the workstation's IP address is arbitrary without specific evidence pointing to an IP configuration error as the source of the problem. Finally, rebooting the switch could cause unnecessary downtime for other users if the issue is localized at one workstation.