Using Apple Hardware Test may help, but two questions come to mind:
  1. You're often unclear about which Mac you're dealing with, so I'll ask if the one in question came with AHT on a disc or installed on its HD, i.e. have you been trying to do something that can't be done?
  2. Either way, did you restart your Mac, or did you shut it down first as per Apple's instructions?

Last edited by artie505; 11/15/15 11:08 AM. Reason: Clarify
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