Sudden shutdown of lenovo u410 laptop, how to find the cause?

Question

Iron

Hello!
Lately my lenovo u410 laptop has started to shut down at random times. At the same time, several things turned out to be characteristic:
1) This happens regardless of the loading stage. Most often, the first time it turns off immediately after turning it on. That is, after pressing the button, the laptop blinks its lights and turns off again, if it boots up, it usually lives for about 15-45 minutes.
2) If he didn’t turn off in the first hour - more, most likely, he won’t turn off. For example, he worked all the New Year holidays without a single failure, after he "warmed up" at the beginning with five or six shutdowns.
3) Shutdowns occur regardless of the power source. Those. both when connected to the charger, and when running on battery power. At the same time, the rules of the game, outwardly, do not change.
4) Shutdowns occur regardless of physical influences, at least apparently. That is, the laptop can stand alone on the table and pass out, or it can go on the subway in your arms and continue to work perfectly.
5) Other deviations from the work of the laptop are not visible. He sees his memory when you need to count something, he cheerfully counts without falling from overheating, I can’t really say anything about the video card - I’ve only tried a couple of toys like tuxracer. Endures them.
From general information: the memory was delivered up to 6g, the hard drive was replaced (maybe two, I don’t remember), the matrix was replaced (not broken, some cable was frayed, now the matrix is ​​​​not native.), Ubuntu 16.04.
Question:
Where to go to localize the problem? Too damn good to replace him. Favorite color, favorite size, favorite cactus.

Answer 1

put AIDA and monitor the temperature. more likely to overheat.

Answer 2

For starters, look at the temperature, then look at the work logs ... what exactly causes the error.