Wow. Okay, so as previously mentioned, your \ key is sticking most likely due to splashing some sugary fluid on the keyboard. Disconnect the keyboard if wired, otherwise remove the batteries. Then pry the \ key up and off with two screwdrivers or picks from opposite sides. A strong thread or fine wire wound around under it should also work. Clean and dry all around the key post with isopropyl alcohol, Q-tips, and compressed air.
Push the key back on and reconnect the keyboard. If it still sticks buy a new keyboard. They're pretty cheap. They used to be fairly tough, but the printed circuits are so thin these days that, left there a few days, a little water can both eat it away and create shorts.