What happens if you install windows over the old one?

Question

Windows

What happens if you install windows over the old one without formatting the partition?
I started the laptop, and there some errors got in, the Wi-Fi didn’t cut it, and then all sorties and that’s it. Now it starts as usual, but at the moment where the password should be entered, just a black screen and a working cursor. The files must be saved, I wonder what will happen if I put a new one on top of the old Windows on the same partition.

Answer 1

The profile files will be copied to the Windows.old directory, the rest (other drive directories) will remain in place