Nothing worked for me. Clearing the CMOS doesnt help at all when secure boot is on, only works if Legacy disabled and Secure boot off.
The only solution that worked for me was opening the whole machine (m6700 in my case with the same problem). Remove the Quadro Graphics card. Remove the Screen Connector.
Attach an external monitor to the D-sub VGA port and you will have the display. Now disable secure boot and enable Legacy ROM and UEFI.
If you are not okay with opening the hardware, just take it to a tech.
This also happened to me on a M4700 laptop with ATI graphics card and the latest A14 BIOS. Fixing it was a pain. Detaching the CMOS battery and draining the power wasn't enough. I had to take out the graphics card, which was no trivial endeavor. The keyboard comes off and then the panel below it, then the display and the graphics card slides out. Be careful about the attached cables, which you'll need to reconnect. Lots of screws of different lengths come out, both on the top and some on the bottom. Below is a video on a different model that shows a somewhat similar process. You can attach an external USB keyboard to fix the BIOS while the keyboard is disconnected. DO NOT DISABLE LEGACY ROM ON THIS SYSTEM; YOU WILL BE SORRY! 🙂