Why does Linux not boot from USB on my HP laptop?

I followed these steps, but can't get Linux to boot from USB on my HP Pavilion dv7 (Radeon HD 6490M). I was told to disable Secure Boot, but that option isn't even in my BIOS menu. 1. BIOS on Laptop - changed Boot Order to this: 1. USB Diskette on Key/USB Hard Disc 2. USB CD/ROM ROM Drive 3. USB Floppy 4. Notebook Hard Drive 2. UNetBootIn wrote the Linux Mint ISO to these drives: 1. A 16 GB USB stick 2. A 60 GB portable HDD 3. Reboot laptop: 1. With the USB stick inserted, it just boots Windows 2. With the portable HDD it says no OS is found on the drive What am I doing wrong?