I was recently searching for a way to recover a non-booting Win8 Dell Inspiron 15R (5520), but none of the procedures worked on my system - ie Right Shift + F8, F8 during bootup, etc... I finally was able to access Recovery Mode and perform an OS "Refresh" which solved my problem by holding down the Shift key (either one, left or right) and selecting "Restart" from the login screen.

I saw where some other folks were looking for a similar solution without success... and I did not see this solution posted anywhere. I finally called Dell Support and with their help got through. Anyway here is another method to try.