Hi:
If you upgraded your PC to W10 from an older operating system, you can clean install W10 as follows...
With another working Windows PC, make a bootable W10 installation flash drive using the media creation tool at the link below.
Unless your PC is very old, it probably is running a 64 bit operating system, so make the 64 bit installation media.
https://www.microsoft.com/en-us/software-download/windows10
If you are asked to enter a product key during the installation process, select the 'I don't have a product key' option, and W10 will install and automatically activate once you are connected to the internet.
If you want to try and recover any files, when you get to the part of the installation that asks 'Where do you want to install Windows,' install it over the current Windows installation, and it will create a Windows.old folder.
After W10 installs, you can explore the Windows.old folder, find your old user profile and copy and paste any folders and files you want to your new Windows profile.