So my MBP (late 2009) has started to show the flashing folder with a question mark in it. I've tried CMD + R , Option, Option + D, and Shift all on startup and all of these keys or key combinations dont do anything. When I press option to boot from a USB with El Captain on it to re install OS X it just pops up with a gray screen and my black cursor and nothing else? I thought it was a HDD issue so I bought a brand new HDD and the issue persists.. I've also tried resetting the PRAM and that hasn't done anything as well.. if anyone could help hat would be greatly appreciated.