What are the status of the important computer files?
Important files can be backed up to another disk drive or the cloud.
If the computer had Windows 10 and had at any time been updated the licensing information should be on Microsoft servers.
Then using a bootable Windows 10 iso Windows can be reinstalled.
Important files can then be restored.
Another method that may or may not work (I've not tested it) is to have Windows create a Windows.old by performing a custom install.
Important files from the Windows.old are then restored.
Find a flash drive that you can format (> or = 8 GB).
Create a bootable Windows 10 iso:
https://www.tenforums.com/tutorials/2376-create-bootable-usb-flash-drive-install-windows-10-a.html
https://www.tenforums.com/tutorials/9230-download-windows-10-iso-file.html
https://www.microsoft.com/en-us/software-download/windows10
https://www.tenforums.com/tutorials/1950-clean-install-windows-10-a.html
https://www.tenforums.com/tutorials/120352-custom-install-windows-10-a.html
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