This time it seems like there's a problem with the memory chip, CMOS battery or the motherboard (hope it's not). It's a 5 y/o laptop which I cleaned every 6 months and measured temp closely, so overheating is very unlikely.

Back then, whenever it boots up and powers off instantly, I usually purge the "flea power" by holding down the power button, and that helped. Not this time though


So I'll probably won't be around much.