Q: Apple Hardware Test won't stop

My daughter went to turn on her MacBook and the Apple Hardware Test came up.  I Googled what the AHT was & so we let it run in order to shut it down.    When we started it up again, the AHT popped up again.  We cannot get it to stop! (There is no disk inserted & she does not even remember hitting any keys that may have started this in the first place.)  Thanks for any help you can lend.