The printer is on a cable but shows as offline
Look at the small lights beside the network socket on the back of the printer. No light means the cable, the port or the switch, so try a different cable and a different port on the router before anything else. If the lights are on, print the Network Configuration Report from the printer's menu and check the IP address it's holding. When that address doesn't match what your computer expects, reserve it in the router's DHCP settings so it stops changing after every restart.