Why did the computer itself reinstall Windows from 10 to 7?

Question

Windows

Initially, the 7th version of Windows was installed. About a month ago I switched to version 10 and the other day there was such a story. I sat in the computer for about 3 hours. Turned it off and went to sleep. In the morning I wake up, he starts to download something without my knowledge. After some time, the installation ended and the computer rebooted and I have the 7th version of Windows. And all the files from 10-ki remained unchanged.

Answer 1

1strange ,

Comp . I gave it to put the ssd and change Windows to 10-ku. 7-ka license, and 10-ku grunted

Well, here are all the questions to where he "gave"
without jokes. absolutely. because you need to watch your batch "at the scene", in the sense of poking around in your computer

Answer 2

The bootloader has been updated, where by default it began to be specified for loading 7 (old) Windows. And it was updated because Win 10 made some kind of major update.

Answer 3

I gave it to put the ssd and change Windows to 10-ku. 7-ka license, and 10-ku grunted

Most likely, those to whom you gave the computer misled you - if the original W7 was licensed, then after the upgrade, W10 is also licensed, you do not need to quack it

Can you write how to run it? (This is the process of downgrading)

Yes, elementary! You need to download the MediaCreationTool20H2.exe program (the digital index at the end of the name may be different) and, with the Internet connected, run it in the licensed W7 (nothing will work in the pirated one). About an hour after a couple of reboots, a brand new W10 will appear on your computer with all your saved settings and software. It is difficult to find this program on the MS website, it is much easier to get it by banal Google.
By the way, it follows from this that there was no need to contact the aforementioned comrades who misled you - everything is elementary done without them.