The proper way to validate an ISO Image you downloaded is to calculate its MD5/SHA1/SHA256 checksum and match it against its published MD5/SHA1/SHA256 value, whichever type checksum was published. If a published checksum isn't available then crosschecking a calculated value with someone else that downloaded the same file and has no issue is an alternative.
The bottom line is verifying the media is the first thing that should always be done in a case such as this and to move forward in a diagnostic/troubleshooting process without first verifying the media is absurd.