Can't boot Laptop from USB stick
I recently acquired a new laptop, an ASUS X551CA. It came with Win8, which I upgraded to Win8.1, and then added some software, inc Office.
I then wanted to backup to an Acronis image, as I do for my other PC's, by restarting using a USB stick and creating an image file.
I've tried using shift + restart, selecting the start with other device option, and specifying the flash drive, which appears as an option. Nothing happens, I just get the usual restart of win8.1.
I then accessed the BIOS, using F2 as in the manual, and altered the boot order to put the flash drive as option 1. Again Win 8.1 started instead.
I am at a loss to know how to proceed, I suspect the BIOS type is set up in some way to force use of the windows boot manager, but I cannot see how to overcome this so as to boot from the flash drive.
Can anyone help please?