T420s - randomly offing itself

[Lockheed]

I have a problemy with my T420s. First, it started randomly generating a signal as if the power button was pressed, so it gracefully shutdown at random occasions, but only when I was typing on the right side of the keyboard. I replaced the keyboard, but it did not change anything, so I just disabled power and suspend button actions (on linux) and it did the trick.

However, two weeks later (few days ago), the laptop started shutting down not-gracefully, ie. it becomes off instantly, without waiting for the system to shutdown. And this time it is unrelated to whether I am touching the laptop, or it is just sitting there. Also, is is not overheating at those times, so we can exclude emergency overheating shutdown (unless the mechanism is failing).
I did memory test with memtest, but found no problem. So at this point I am ready to assume it is motherboard's fault and am planning on replacing it.

If anyone has any other suggestion, please chip in.

Anyway, as I am doing so, I am musing on replacing it with Intel-only GPU, since Nvidia is only 20% quicker, eats more battery and causes problems when connecting external monitor through DisplayPort.

[Hans Gruber]

Pull the bios battery for 30 seconds and plug it back in. Reset the bios to factory default settings and maybe hold the power button down for 10 seconds 10 times for good measure with the battery disconnected.