Burn the ISO file which you downloaded to DVD using ImgBUrn at 4x speed. ImgBurn - Free software downloads and software reviews - CNET Download.com
If it fails, download another and try again.
You can also write to flash stick using Universal USB Installer
with Win7 in dropdown menu. Boot under USB, Removable or HD's in one-time BIOS Boot Menu - set HD to boot first in BIOS setup.
Adapt these steps for getting a perfect reinstall of factory OEM to do your booted Pro Upgrade install: Reinstalling Windows 7