The Collaborative International Dictionary of English v.0.48:

burn out \burn out\ v. i.
   1. To burn till the fuel is exhausted; as, when the candle
      burned out the room was totally dark; the firefighters
      couldn't control the oil tank fire and had to let it burn
      out by itself.
      [1913 Webster +PJC]

   2. To stop functioning due to failure of some component
      caused by the heat of the electrical current used in its
      operation; -- of electrical devices.
      [PJC]

   3. To become apathetic or depressed, and cease to function
      effectively, due to the fatigue and frustration of
      prolonged stress and overwork; -- of people; as, the
      stress in the bond market is so great that many traders
      burn out after only ten years on the job.
      [PJC]

WordNet (r) 3.0 (2006):

burn out
    v 1: melt, break, or become otherwise unusable; "The lightbulbs
         blew out"; "The fuse blew" [syn: blow out, burn out,
         blow]