Laptop switches off by itself?

I have the problem that my laptop switches off by itself (immediately after starting) an overheating is not the reason I had the problem before and went to Saturn they repaired it and then it went back after a few weeks since I had the laptop again use it starts again.

Laptop: Trekstor Primebook p14b.

Then ask at Saturn what was repaired. Without checking the device, it can be anything and everything!

They installed a new mainboard.