I have a Dell Inspiron 5537 running Windows 10. Yesterday I tried to get to the boot menu from the reboot process by pressing the F12 key when that message comes up on the screen. It never worked. I could get to the set up screens by pressing the F2 key. The F12 key works when booted up to change the volume so I don't think the key itself is broken. I wanted to make the laptop boot from a Macrium Reflect recovery disk to see if the disk was working (for another fun troubleshooting project on a Dell desktop). I searched and searched to find an answer to this problem with no luck. I did find a Dell response to a query about this saying that the reboot is often only a partial reboot to save time and I have noticed this on my laptop. Unfortunately the instructions for how to force a full reboot were for Windows 8 and didn't work on my computer.

I'd really like to know the answer to this in case I ever need to do boot from some other device (CD, USB).

Thanks for your help.