Toyota Repair: 4 runner wont turn over, alternator, headlights

Question
My buddy's 4 runner was down for a week because of a bad alternator.  I went over and replaced his alternator for him and gave him a jump.  His 4 runner was running good for about 15 min. and then just died out of no where.  It will not turn over now.  His headlights still turn on and are bright so the battery is good.  is this problem alternator related or something different?

Answer
I don't think it's the alternator because the battery is still good so it seems to be charging the battery. Recheck the battery post connections make sure they are tight, if the starter makes a clicking noise but not turn the engine over then the starter is the problem.