WordNet (r) 3.0 (2006):

conk out
    v 1: stop operating or functioning; "The engine finally went";
         "The car died on the road"; "The bus we travelled in broke
         down on the way to town"; "The coffee maker broke"; "The
         engine failed on the way to town"; "her eyesight went after
         the accident" [syn: fail, go bad, give way, die,
         give out, conk out, go, break, break down]
    2: use up all one's strength and energy and stop working; "At
       the end of the march, I pooped out" [syn: poop out, peter
       out, run down, run out, conk out]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "conk out":
   be done for, be no more, break, break down, cave in, cease,
   collapse, come apart, come to naught, come to nothing,
   come unstuck, crumble, decline, die, disappear, disintegrate,
   droop, drop, end, expire, fade, fade away, fail, faint, fizzle out,
   flag, flame out, give out, give way, go, go dead, go downhill,
   go haywire, go kaput, go soft, go to pieces, go wrong,
   hit the skids, languish, lose power, pack up, pass, pass away,
   peg out, perish, peter out, pine, poop out, run out, sink,
   sputter and stop, stall, stick, succumb, vanish, weaken, wear away,
   wear thin, wilt, yield