Laptop shuts off: after boot up, when plug out, & stressed

My laptop Lenovo IdeaPad s206 shuts off with any of the following scenarios:

1. AFTER BOOT UP
The laptop will boot up normally until the desktop but will loose power for some reason. (Sometimes it shuts off during boot)

2. PLUG OUT

When I power on the laptop and pull out the plug, the laptop will loose its power even with the battery fully charged.

3. STRESSED?

I think when it does something that makes the CPU work hard it overheats and shuts off to protect itself or receives insufficient power from the PSU?

HISTORY
This laptop is 3 years old. It originally has Windows 7 upgraded later to Windows 10. I didn't get any problem with Windows 10 unlike the others, but one month after that I shuts off instantly. I turned on the laptop immediately and boots up like nothing happened then it shuts off again. I tried to use system restore but there wasn't any restore point saved.

Repeated on and off probably caused to BSOD. I searched for possible solutions on the internet. The BSOD originally says "BAD_SYSTEM_CONFIG" or something like that, so I tried all the methods I found but they all fail.

It got worse as time goes by, because now it only lasted seconds before it looses power and it doesn't power on when it's not plugged in, or shuts off immediately when plugged out. I loose hope and stop messing with it, we also have another PC so that's what I use now. I didn't bother with it for months

Months after that I decided to revive it again and for some reason, the power stays even when I unplug it so I got motivated and searched for hardware solutions this time. I checked the fan it wasn't that dirty, so I cleaned the fan and also replaced the thermal paste. There's an improvement it doesn't shuts off unless for some unknown reason it does. I also decided to do a hard reset on it which get halted due to instant lost of power during process time. Persistently hard resetting it and finally the process went through, but it stated that "reset failed" at the end.

When I boot it up it was empty, so I decided to install Ubuntu 14 LTS via USB. It did great I mess with it a little, until there was this update that pop up. I clicked OK but after that nothing seems downloading or happening(I don't know how to use that OS), so I persistently try to update it, then a pop up something about updating the list I click OK again but still nothing. It then hangs and shuts off immediately.

I'm back to my old problem. The power looses when I unplug. I turned it on and try to update or do web browsing, and whenever it got stressed it will shut off immediately. It got worse because now it only managed to finished the boot up until the desktop before it shuts off immediately.

----------------------------------------------------------------------------------------------------------------------------------------
Some conclusions and questions

I noticed that it doesn't shutoff when in BIOS, but still do if I unplug it. I even tried leaving it in BIOS for one hour(it can probably go for more) and the laptop is hot but its still going, so maybe overheating isn't the issue? I also did USB boot Ubuntu and the shutting off still happens, so the hard drive or operating system may not be the cause?

Is it possible for a faulty RAM or hard drive to be the cause?

What if it's the PSU that's causing the problem?
__________________________________________________________________________________

Why I didn't just go to the repair shop?

- I did and ask them about the possible problems or causes. I also want to take this opportunity to know more about my laptop, so I can maintain it on my own. They are charging a lot for something that I may be able to do myself. If something breaks while messing with it then maybe that's the time I'll give it to them. Going to the repair shop is the last thing for me to do.

___________________________________________________________________________________
FINAL REMARKS

I don't know much about computers. The knowledge and everything I've done here is based on my research from the internet only. I would really appreciate it if you could give me something that could help me to solve my problem.
 
A 3 year old laptop does need some "loving" care. The thermal pads or paste on the CPU and Graphics chips dries out and can cause shutdowns. A bad battery can do this too, after 3 years. If you haven't tried running the laptop with the battery removed, try it. If the shutting off stops, replace the battery. If the laptop still shuts down, you may look into getting the laptops thermal paste or paste replaced
 
Cleaning fan may be insufficient. When changing thermal paste, look for dust blockage under the fan shroud and at any screened intake or output locations. There are very good videos on YouTube - and there may even be one for your specific model. Just be sure to put it back the same way and you took it apart (some screws look the same but can be longer!!).
 
Back