if htis is an intermittent problem it's hard to diagnose on here, only thing i can tell you is to eitehre when it happens hit starter with hammer on body of starter, if it starts yo may have a flat spot on armature otherwise it's best to check to see if it's getting power when it doesn't start by a pro because he can check the whole system out. You could have a bad or weak battery and have thea tested for load and condition. auto parts do i for free