Hey. I got a used computer that looked perfect, but after a few weeks I realized I couldn't change the wallpaper or use some features. It turned out the system wasn't activated. The seller wasn't helpful, so I started searching online and find out https://www.dailywaffle.co.uk/2021/03/the-evolution-of-windows-os-infographic/ . The site had clear information on why this was happening and how to fix it. I followed their instructions and my laptop was fully functional again.