bro i also had the same problem but i tried it by my own method when you turn on press F12 as the moment you see dell symbol Then i dont rember the exact but select last option below bios setup then after reaching there ther will be futhur two option you try both one at a time while doing this you will see dell  warning to change that setting but you do that .It worked for i too search the  whole internet but didnt found the solution anywhere  but this my method worked  for me hope it  will work for you