How to boot from a usb in UEFI mode on a Dell Inspiron

I've had the same issue for 1 year now on my Inspiron 5567 Kaby Lake 7500U.

The secret to install Ubuntu/Debian/any linux distrib on new Inspiron 5567 Kaby Lake is here: you need to create a special boot setup.

For a dual boot with a Windows 10 preinstalled :

1. Burn your iso with Rufus (mostly GPT mode for laptop after 2013, config autoselected by default in Rufus. Change to MBR if the pc is older),
2. Go in your USB key and enter the EFI and please notice the name of the files here...as grubx64.efi (unsecure boot) or shimx64.efi (secure boot). You will need this info later.
3. Restart the PC with the USB plugged in. When the Dell logo appears, hit F12 till you see the boot menu. If you can see your USB key here, don't select it. First, enter the BIOS by selecting bios setup.
4. Go on Boot Sequence, you need to ensure the BIOS is set to UEFI, disable Legacy option ROMS and check that secure boot is enabled on the Secure Boot Enable line.

5. Now the most important operation... come back to Boot Sequence (General menu on the left)

   • click on Add Boot Option. The Add Boot Option window will pop up. Type a name in the Boot Option Name text area ("Ubuntu", for example).
   • Click the button to the left of the File Name text area. The EFI Boot Selection window will pop up.
   • In the File System drop down menu choose FS0: and EFI. Then using the directories section, navigate until you can choose SHIMx64.EFI (for Ubuntu only - for other distros use grubx64.efi or grubx.efi if your PC is not amd64, anyway it will be named grubxxxxx.efi) in the Files section.

6. A new boot option will now appear on the top and in the boot menu. Save and exit

7. The pc will now restart, when the Dell logo is coming, press F12 again, till the boot menu appears. Select the name you entered in the previous step (NOT the USB key)

8. The GUI installer will come up and you can run it

If it does not work for you exactly like this, try disabling secure boot in the BIOS.

You don't say what tool you used to create your USB drive. This is a critical detail because not all boot programs are created equal. Rufus and Unetbootin usually work well for creating EFI-bootable media, but this varies somewhat from one computer to another, so even if you used one of those you might try something else.

Another option is to install in BIOS/CSM/legacy mode and then install my rEFInd boot manager from Windows. This will require that Secure Boot be disabled, but once rEFInd is up and running, it should enable you to boot Ubuntu.