Win8.1 64 won't boot up-BSOD-WHEA_UNCORRECTABLE_ERROR

I have oc'ed my 2600K 1 week ago to 5.1Ghz and I ran some stress tests(at the same time I updated to win 8.1 too), etc. Everything seemed to be working good without problems. Yesterday I bought a new GPU to install it on my MB so I could connect more monitors because I had reached the limit on the original GPU(GTX560). At first it worked good without problems but after two hours I had received a BSOD(WHEA_UNCORRECTABLE_ERROR) while I was playing a game with friends....however everything was going smooth as you would expect. After that the computer restarted and I logged in and there you go I got another bsod after like 15mins from logging in. Next login I got another BSOD after like 10mins. It kept decreasing till this point where I can't even see the login screen. After a lot of attempts to get into the computer just to do something, like drivers..etc, but everytime I try to get into safe mode I get the bsod again at the time where you choose the settings(IMO the windows 8 safe mode settings are so annoying). I could eventually figure out that it had something to do with CPU. So what I did is from the BIOS I let CPU use only 1 core and it let login normally at first but I had around 5mins before it got another BSOD. On safe mod however, it stayed without problems. I also want to mention that BSOD occurs on different temps, sometimes on 40C(CPU temp). So my question to you do you have a clue about what is going on?

Here are the things I tried:
1. I unplugged GPUs and tried without them, nothing changed. I even used the on board GPU.
2. I removed all extra PCI cards and swapped rams..with no help..
3. I did load optimized default settings from BIOS. I also did a CMOS reset, still nothing.
4. I have now taked the MB out of the chassis and trying out further experiments.
5. I have ran a Live ubuntu installation...and I received this error similar to this one(NOT EXACTLY!):
http://askubuntu.com/questions/194796/installation-problem-ubuntu-12-04-crashing-hardware-error
6. I have now taken out the CPU cooler and changed the thermal paste and installed it again, nothing got better.
My PC specs:
intel i7 2600K
x2 4GB 1600MHz Vengeance
MB: p8z68-v gen3

Note: I have also installed a new CPU cooler one week ago when I did the OC, but the temps were really normal on load(60C-75C).

Thanks in advance