Laptop turns off & on again at random

I don't think it is turning off and back on. If that happened, windows would reload and you would not be at the same place everytime. Also if the computer were rebooting (sometimes people say turns off and then on when they mean rebooting), again windows would start to load again.
I suspect the screen is blacking out. Attach an external monitor and keep both displays working, the laptop and the external. If the laptop screen blacks out, does the external also? If so, the video chip could be failing. If not, then maybe the backlight on the laptop is failing. A backlight display can be fixed. It can be expensive but it can also be cheap if there is a do-it-yourselfer around who can replace the capacitors. If it is the onboard video chip, there is no solution. Once that goes, it isn't like a desktop where you can install a video card and use that.
A few notebooks do have a replaceable vidoe card but it is very few and I don't remember the brand nor model.

 

A computer that overheats doesn't turn back on immediately - that's how you rule out a heat issue. If the computer overheated, it takes a while for everything to cool off before the computer is willing to boot up again.