Sounds like a bad DVD.
Did you check the SHA1SUM of the file that you downloaded? This is very important, particularly with large files. Perhaps try using bittorrent, as this can result in more reliable downloads. With bittorrent, each segment of the file is checksummed, so if one segment has an error the whole file does not need to be re-downloaded.
Also, while some say it is an urban myth, burn the DVD at a lower speed in Nero.
You have obviously burned the DVD correctly, as otherwise it will not boot.
I hope this helps