Hello! My name is***** am a computer professional with over 15 years of experience with both Mac and Windows computers, phones, tablets, e-readers and printers. I would be happy to help you with this. It sounds like have two different issues. What are you having trouble logging on to? A Kindle? You should be able to find the serial number and model number by logging into your Amazon account using the link below:
On the page that appears next, you will see a CONTENT Tab and a DEVICES Tab. On the DEVICES page you should see your Kindle listed with a serial number and a model. Please let me know what you see there.