Read other threads if you want to make more use out of your 4163B.
Don't abuse generous RMA policies.
If you can't see the serial number, ask the guy who sold the drive. If the person does not answer clearly, ask for a refund. So, is your drive OK or not? If you want to make sure whether it's your drive, or media problems, or PC problems, read other threads and/or do some tests that suit your situation.