1. How did you "burnt the ISO to DVD"?
2. What is this PC? On an Asus here the USB DVD does not show in the BIOS but for that machine I have to power on and hold down the Esc key to get a boot menu which the USB DVDRW shows up on.
I've lost track of how many folk burn the ISO file to a DVD. It's tough for some but we do is create a DVD from the .ISO. The difference is subtle but important.
I have had Windows 10 downloaded as an .iso for awhile and just decided to try and instal as a dual option with Windows 7 on a separate drive. However having burnt the ISO to DVD I have now found that my DVD drive does not show as a boot option in my BIOS. This is a bit strange as I previously gave Windows 8 a try and installed in a similar way, so what could have changed to alter the BIOS settings? The drive shows up in computer and loads automatically when inserting a disk.