Win10 incompatible hardware install

[paul.deitch]

One of my friends brought a laptop round today which her brother had decided to "do her a favour" and install Win10 on it over Win8.
It just keeps rebooting.
I took a look at it with a Linux disk and it looks like there is still some info on the disk.
Then I checked out the laptop and found that it is not compatible with Win10.
What's the best way to proceed and not lose the existing data?

[Harpoon]

I'd pull the drive out of, connect it to another PC via an appropriate USB caddy to copy off the stuff, then put the drive back and wipe it for another install.