I have a Dell Inspiron 15R SE 7520 with A11 version of BIOS, latest from dell.com. I decided to reinstall Windows 10 from USB stick which is formatted to FAT32 and is bootable.
The issue is that I am unable to choose USB boot from the menu when pressing F12. I tried under both UEFI secure: ON and Legacy boot, but it does not want to boot windows at all. When the usb stick is plugged in it stalls at the dell logo. When it is not it normally runs my already installed windows 10. Under UEFI boot settings there is only 1 option - the windows itself. Under legacy boot options theres only HDD and Network (when switched to legacy boot option). I have both tried Microsoft Media Creation tool and Rufus to create the bootable flash. It is the same every time - stuck at DELL logo screen and unable to boot the installation. Please help.
You might try another USB port. The drive has to be available to the system during the initial boot, prior to the Bios. If it is on a port which isn't being started during boot, it will not be seen.
Just in case, it does take a 64 bit Win 10 version to use UEFI.
Where did you get the .iso file you are using?
I am using Windows 64bit for sure. And i tried all of my usb posts. 3 of which are usb 2.0. One is 3.0. I got the iso through Microsoft's media creation tool.