Blinking question mark on folder on boot
If only the arrow comes up when you hold down option it most likely means there's some kind of hardware issue.  You may be able to repair it using the Disk Utility in Internet Recovery (Hold down ⌘ command+⌥ option/⌥ option+R while booting) , but I'd advise in to looking to getting this thing serviced or repaired.  Sounds like you've got a bad HD.  

If all else fails, run fsck and see what happens.  Information on how to do that is located also in the provided article.