What was its issue? The battery turned out to be worn out. So when the battery is too low it took 15 minutes on power before the power button worked. Another Dell had a BIOS update that mysteriously fixed the iffy power button.
Given the laptop is 5 years old, did you try a new battery?
I have an ASUS S400C, and the power button has started to go. It has a power on when lid opened feature which I use, but if the power ever fully goes (which happens as power goes out in my office a lot) it takes about 20 tries to press the power button and get it back on. It otherwise functions fine. I have the most recent BIOS update, but so far as I can tell the ONLY power option that I can access is the lid power opening. I've seen screenshots of UEFI utilities from ASUS and also from the same era (2012-ish, my last BIOS update I just flashed was from 2014) with WAY more options. Are they just better motherboards? Sorry I'm a bit dim at all this but generally can deal with these things. I also live in a developing country where I really don't trust a tech to take it apart and replace the button, it seems to just be a hardware issue. I'd like to bypass this with AC power however if possible. Just surprised to not see it as an option!