I had the exact same problem the other day! For me it was because my RAM was running at 1333Mhz and not its actual 1600Mhz (I don't know why this stops the PC from booting properly, but it does ). So boot the system (so in your case, remove one stick to allow it to boot normally) and load the BIOS, change your RAMs clock speed to what it should be, rather than the motherboards default. Put both sticks back in and viola!