Hi I have a question. I bought my computer a few years ago. It came with windows xp, had a free upgrade to windows 7. I then purchased a windows 8 pro upgrade disk, installed that, and now I am running windows 8.1. Fast forward a few years, I've changed my computer case and lost everything but my windows 8 pro upgrade disk. I've read that you can not do a clean install with this disk without installing previous versions. What is the process of installing 8.1 and making sure my copy is valid and working. I want to totally reformat and start over fresh, but am worried that my key will not work if I install from the windows 8 pro upgrade disk. Thank you for any help.