Question PC artifacting, freezing, shutting down itself

[VarunB87]

It started with some weird, square shaped artifacts showing up on desktop background & photos viewer on several occasions after I had started overclocking my 8600k. Even Youtube videos had weird green lines. Increasing the Vcore would take care of that but the artifacts would not go away even when I upped it to 1.4V for testing. Removing the overclock solved it. However yesterday, my computer refused to boot even on default clock speed & started showing the following symptoms:

• booting till Gigabyte logo screen & then turn off automatically .
• booting till startup screen & then turn off automatically .
• turning off/freezing automatically while navigating in Gigabyte bios. It does not even allow me to select the bootable USB for memtest.
• freezing in Windows after logon within a minute & then turning off automatically . Sometimes it would remain frozen but would not turn off.
• artifacting on startup screen, desktop background & photo viewer before turning off.
• freezing during memtest execution that I was able to get into today.

Here's what I did:

• cleared CMOS & load optimized defaults.
• tried memory module one by one.
• tried different PSU.
• tried turning ON computer with IGFX after taking out my gfx card.

Nothing worked so far. I am beginning to suspect that either the CPU or the mobo has gone bad because the computer is turning off even in bios. I would like to know what you all think before I head to the service center for it. My computer's specs are in my signature.

Image capture of the artifact:

https://imgur.com/r4eUoP4

View: https://imgur.com/r4eUoP4

 

[helpstar]

reseat the ram and CPU

reset the CMOS by jumper clrCMOS

 

[VarunB87]

I had already done that as stated in my original post but the problem still persists. I was somehow load into memtest & that too froze during the execution. I am now leaning more towards faulty CPU.