Un-updated windows versions have an end of support date getting nearer on a daily basis. Updating to W10 is only free for a few more months. It does work better than either of its predecessors even if there is a bit of unwanted dross loaded with it, which is removable. It is no longer an "experiment" for pretty much everybody, but a fully working system that does seem to work faster on the same hardware.
I really can't think what might be wrong with Captain Podges machine, but something is. Maybe something plugged in a USB hole that it keeps trying to reboot from? All of mine I simply pressed the "yes, go ahead" button and let it do its thing, apart from the bit where preferences get set. Just seen the new post - maybe using a wifi connection instead of being hard wired to the router?