Hello,

        Seems your not alone, if you would take a look at the links please.

http://productforums.google.com/forum/#!search/Galaxy$20nexus,$20power$20button$20issue/mobile/NiBXEjx6G6g/GhMQolqJUuIJ

http://productforums.google.com/forum/#!search/Galaxy$20Nexus$20power$20button$20doesn%27t$20always$20work/mobile/_XXKL7-cc1Y/gaHM4BG_4a0J

http://productforums.google.com/forum/#!category-topic/mobile/android-devices/rkbvoQ0tf-k

  And think it is a known problem, but not sure if their is a fix, in the posts a few people told of possible solutions, but never had that problem on
any Android phones and many had ICS on many of them, but no more!!!! Upgraded to HTC shut off updates as the next update was ICS. Can't take that chance any more last pair of Nexus S cost me over one thousand dollars + to break contract and get away with ICS and found an Android O/S that has No problems.

     Good Luck