6y later since this issue reported and now I got it, just some days ago, after a normal shutdown before I went to bed, next evening I could not power it on. I. also searched on the internet and saw the solution by pressing concurrently two button Thinkvantage and power (of course I have performed power reset,... previously). But, after the 1st solving, now I got the problem again after 1 night. As checked, Thinkpad t420 in good conditions of adapter and battery. Don't know it relates to ram, ssd,... Don't know it relates to CMOS battery?