Why does my laptop randomly turn off?

Question

Do it yourself

There is a laptop HP G62 b50SR. It worked properly for about a year, and then overheating and brakes began. Took it apart, cleaned it, changed the thermal paste. Then he worked properly for another 2-3 months and again the same problems began to appear.
After a while, it generally began to periodically turn off, regardless of the load. Let's say I went into the BIOS settings at startup, and it turned off after 5 minutes. BIOS settings do not create any load. After turning it off, you need to let it stand for several minutes, because it does not want to turn on right away. The average temperature before shutdown is 70 degrees (speedfun, cpu).
Worn for service 2 times. At first, they simply changed the thermal paste for thermal pads. It did not bring any effect. In another SC they said that the problem was with the north bridge. Changed. At first, there seemed to be an effect, it worked stably for some time, but six months later, all the symptoms recurred.
I can not understand why such degradation after a year began. Initially, it was generally quiet and fast, but now it constantly accelerates the cooler and turns off.
PS I don't think copper plates/thermal paste/thermal pads should be recommended. We are not trying to overclock, but to make sure that it does not turn off. Very disappointed in the service centers. No one really wants to understand the problem (what we call "debugging"), they just try to replace alleged problematic elements by typing.

Answer 1

Let's say I went into the BIOS settings at startup, and it turned off after 5 minutes.

While working in the BIOS, the processor power consumption is maximum. No energy saving works yet. Here it turns off from overheating.
Overheating of the processor, again.
Looks like the radiator is bad. Try replacing.
A thermotube is not a piece of copper, but a tube partially filled with water, air is pumped out of it, the boiling point of water in it is 40-50 degrees. If a crack appears, the water evaporates, the thermotube becomes just a tube. Overheating starts. Read about heat pipes on the Internet before buying a new radiator.

Answer 2

set Linux
to work
catch reboots
read logs
, maybe also try to read vin-logs
Ideally - hand over under warranty so that the laptop is completely changed