M6700 blank screen during Secure Boot

This is how I unlocked a Dell Precision M6700 laptop with blank display at power on next to enabling secure boot in BIOS version A20.
The issue is the lack of power on display (dark screen) to enter BIOS after enabling secure boot via F2 or F12.

1. Unplug all peripherals
2. Power on the Dell laptop computer and immediately frantically keep hitting and releasing the F12 key for about 2 MINUTES !!!
3. Hit the DOWN key 10 times = ten times
4. Frantically keep hitting and releasing the ENTER key until system restart
5. After keboot the POST Dell logo appears. Hit the F2 key to enter BIOS setup or F12 for boot selection!
6. Disable Secure boot in BIOS
7. Save BIOS settings and exit

Hope this helps !

"5. After keboot the POST Dell logo appears."

No it does not.  The K4000m graphics card has firmware that doesn't support EFI, so it will not display anything, not even the logo.  The display does have power (not dark screen) which can be verified by doing a screen test:  Press and hold the keyboard's "D" key before powering on, which will test the screen instead of booting the computer.

On the other hand, I've read that if the screen is sufficiently low quality then there's a way to bypass the K4000m graphics card and use the low quality Intel graphics chip instead.  A screen swap should be easier than removing the K4000m graphics card and attaching an external monitor.  After disabling secure boot and enabling legacy option ROMs, you can swap back to your original high quality screen.

Thank you! This solution worked for me on my Dell Precision M4700 with Nvidia graphics after unsuccessfully trying to reset the CMOS battery or any other solution proposed. 

I thought this was a joke but it worked! KUDOS!