Thanks Mikey As I understand the boot order tells the mb which device to boot from. To do this I think i need to put usb 1st in the list. Failure to do so means that the mb will try to boot as on my set up from the DVD then the ssd drive followed by the SATA drive. I can't find any reference to usb on the mb to move to first boot. I d/l windows 10 Iso and wanted to boot from this to install windows
some motherboards/bios gives you the option of selecting a temporary boot device,
during bootup you may see a messege on the screen briefly saying something like "press F12 for other boot options"
make sure your USB is plugged in while accessing your bios, it may not give you the option of USB in the boot order unless the USB is plugged in,\
other then this you might have to play around with other options in the bios to enable the USB boot, and everytime you change an option you will need to save and exit and reboot,
if the boot order is giving you the option of CD boot, then you could create a bootable CD instead of the USB