To turn off an electrical appliance or device (esp. Computers or Tv's) by cutting its power; either by pulling the plug out of the socket or flipping the switch, instead of following standard procudure (running Shutdown, pushing the power button). Nuking can happen accidentally or deliberatly.
To cook something in a microwave oven. "Neuked" to have beencooked in the microwave. Neuking-the act of being cooked in the microwave.(Note the spelling change when the word becomes a verb or adjective)
Derived from the common belief that Microwaves were like Neuclear Power and had supernatural properties that could bring Frozen meals to life in a matter of seconds.