Question Windows PC turning off unexpectedly

Jul 24, 2020
Hi everyone, I need some advice!

I built a desktop PC last year and it has always run smoothly until a couple weeks ago.
It started turning off unexpectedly, but not just suddenly shutting off like somebody had turned off the power switch, because the Windows "Shutting down..." screen normally appeared.
At first this was just happening once in a while, but then it started to be more frequent. Right now I can sometimes keep it on for five to ten minutes, but when it shuts down it keeps turning on and off for about 15 seconds before dying completely. At this point I have to wait a while to restart the cycle.

I initially thought of a overheating problem, so I changed the thermal compound, logged into the BIOS and checked the CPU temperature. It rises constantly from about 45°C to 75°C and then shuts down.
So I tried to boost the fans: it rises to 57°C and stays still for a while, but then the PC shuts down anyway and begins his on and off cycle.

I have to say I am a bit rusty on hardware and system troubleshooting, so I'm asking you all for a little help.
Do you have any idea on what might be wrong?

These are some of the PC's specs, by the way:
  • Motherboard: B350 Thomahawk Plus
  • CPU: AMD A10-9700 with Radeon R7 (I never changed the CPU cooling fan)
  • PSU: Corsair VS 550W
Let me know if you need any other information!

Thank you all in advance!