You must turn off the HP Officejet 8710 printer offline  to resolve the HP Officejet Pro 8710 Offline issue. After that, you have to wait for about 10 to 15 seconds. Additionally, unplug the printer's power supply and also, turn off your computer system. After some time has passed, reconnect the power cord to the printer and switch it on. Then, restart the router if your printer is already linked to a wireless network. At last, turn on the PC.