Computer boots with only 1 active core?

Question

Iron

Hey!
Yesterday there was a bluescreen, after which the computer stopped loading (as if overclock failed all the time, even with completely stock BIOS settings)
Sometimes windows still started loading, but only reached half with the bluescreen WHEA UNCORRECTABLE ERROR.
At random, it turned out that if you put a limit on 1 core (instead of 4x), the system boots and works stably, even with overclock = \
Question - change the processor or motherboard?
System:
Core i5 2500k running at 4.7GHz (corsair h100 cooler)
Gigabyte z68xp-ud3 rev1 mb
win8 pro
The memory test did not reveal any problems with the RAM, so I don't see the point in listing something else here, but if it's important, check it out!
Thank you very much in advance.

Answer 1

Most likely - a marriage of either a processor or a slot on the motherboard. Well, or something is wrong with Windows.
Try:
1. Replace the processor with a similar one.
2. Insert the processor into another PC, or replace the motherboard with an analog one.
3. Run (from Live CD/USB) any of Linux or WinPE.
The results will make everything clear.

Answer 2

Should I reinstall Windows first?