Inspiron won't recognize bootable USB

Question

I have an Inspiron 7720 17R,Windows 8. I'm having problems with Windows so I want to start from scratch, i.e. a new install of Windows. I have a 2 bootable USBs, one created soon after I bought the computer with Dell Backup and Recovery, and a 2nd USB with a bootable iso file with Windows 8. I tried both (not at the same time) and both did not work. I booted the computer, pushed F12 many times, and got into the boot options. Booting from USB was not there as an option so I used F2 to create an option to use a USB to boot. Unfortunately when I choose my own created USB option the system ignores it and goes into normal startup. The normal startup on my laptop is UEFI, secure boot on. How do I get my laptop to recognize a USB  to start so I can remove everything on my laptop (including my accounts) and start as if it was a new Dell laptop? Thank you.