If you burned the ISO with Windows 7 that has WinZip installed, it might have literally burned the ISO as a file. Windows 7 has the "burn ISO" as a default choice when you right click the ISO, but I have noticed that when WinZip is installed it steals the file association for ".iso" which causes Windows 7 to burn ISO as regular files after the association is taken. On my Windows 7 VM, I had to re-associate ISO files with Window 7 Burner to fix the issue.
I would imagine that if any program steals the ".iso" file assoiation then the result would be the same.
I think if the MD5 is correct, re-downloading would not make any difference.
Im just grasping at straws since you said you cannot boot and you also cannot see the files that should have been installed to the DVD.