I would check using md5sum
check sum to see if your download ISO is valid. This is the md5sum for Fedora 20 'b52130db4067e3e7acf621653abce7ec' You can get this same check sum from Fedora for the version to be tested/compared.
If that does not compare then I suggest to get a new download & check again. You should burn the ISO image at a slow rate, 4 has always been successful for my burner. Takes more time but insures a valid burnt image.
Hope this helps.