You need an ISO image file to burn to DVD using ImgBurn at 4x speed.
Just burning the files to a DVD will not make it bootable, which you need to wipe the HD, partition and format before install.
Check to see if you have an ISO file and if not download one from your source.
Here are tips to get a purrfect clean reinstall of factory OEM - use the ones which apply: re-install windows 7
Remember that to install Upgrade version to a cleaned HD you'll have to leave the key blank during install, then afterwards do the quick registry workaround here to activate at Computer>Properties link: Clean Install with a Upgrade Windows 7 Version