I just got a brand new computer, which comes with windows 8 (not pro), but I use an application that can only run on Windows 7 pro; thus, the need to downgrade. I have a Windows 7 Pro DVD (designed for upgrading from vista) but I can't use the CD drive. Is there another way to install from scratch with no DVD?
You can burn the Windows ISO image to USB flash drive and then boot from it. You have to change the boot sequence form your BIOS settings. Most of the time, you have to press DEL or F8 or F2 button while booting. Depends upon your motherboard brand. Then set your first boot device as USB drive and boot from it. All next steps are as usual.
You can use Rufus or LiLi or Windows official bootable USB drive creation tool to burn the ISO image to your USB drive. The drive should be more than 4GB in size.