Stop 0x00000101 BSOD during heavy CPU use

Hi All! I have been working on fixing up a PC for a basic gaming rig for my son. I managed to cobble together some parts and have got it all up and running but now im having a problem. Basically when the CPU is under load it either freezes or it blue screens with the error Stop 101 which I believe is related to the CPU? Anyway this happened a lot when I first inherited the board but after a BIOS update it seemed to stop happening. I used PRIME 95 and confirmed that the problem had gone away - played many games since then. Recently I upgraded the memory to 8Gb from 4Gb and slowly but surely the problem has returned to the point where I can't run a single game without an almost immediate blue screen, restart or lockup.

The CPU fan and heat sink are clear of dust and have had thermal pasted replaced properly. Also the CPU is reaching around 40C when it crashes so it's not a heat issue.

The motherboard is an MSI 870A-G54(FX) with 8GB DDR3 Memory - it was running at 1600Mhz (the max the board can take and requires the board to be overclocked) but I since reduced it to 1333Mhz to see it I helps (nope). The Memory is Corsair Vengeance 2 X 4Gb and The CPU is an AMD Phenom II x6 1100T

Im using Windows 7 Home premium at the mo.

Basically I was wondering if there is any way I can test for sure if this is the CPU that's failing or if it's the Motherboard? Any Advice I can get would be great.