1) ok what computer are you using and what is the hardware specs and how old is it.
2)what did you use to format the usb my advice is use a program called rufus ( http://rufus.akeo.ie/
3)what did you use to make the DVD bootable if i it is a retail version it should work (if you torrented it i want judge you
4)were did you get the ISO image for your windows image also rufus can rip files from a disk onto a USB and make it bootable
my advice is use a usb it is quicker and better even my old HP laptop can boot from usb it is from 2004 a pain but doable