Random freeze after OC - no bsod

[c4su4lty]

Hey guys,

I have been trying to overclock my CPU for over a week now with average success.
So far I have been able to keep 4,4Ghz stable at average 60-65°C and 1,3V Offset - I run Prime95 for hours without any problems.
Only thing is as soon as I transition to everyday use, my computer freezes and I have to hit the restart button.
No Bsod, no sound (except sometimes a stutter soundloop).

Even after a mild OC of 4,0Ghz this issue occured.

Yesterday after freezing again the computer didnt boot properly.
All signs pointed to a broken RAM but after a while it worked again.
I was so happy because a broken RAM would have explained a lot.
I will test the Ram with Memtest later, because when I try to boot it from a usb stick all I get is "Boot Error".

So what am I looking for?
I want a proper stable 24/7 OC without any freezing.
So far the OC worked except for these random crashes.
I've been searching the whole internet and so far nothing has worked.

My rig
Mobo: AsRock Z68 Pro3 updated to Bios v2.1
GPU: AMD Radeon 7970 DDR3
PSU: Corsair TX650W
RAM: 2x4GB Corsair Vengeance (removed heatsink)
Sound: Asus Xonar DG
CPU: i5 2500k (bought it in 2011, never OC'ed it till a week ago)
Cooling: 3x120mm fans plus Thermalright Macho Rev A
2x HDD, 1x SDD (installed win7 two weeks ago)


The changes I have made:

 

[Zerk2012]

That board does not have a very good power delivery, first thing I would do is raise the northbridge voltage a bit.
Cant see any of those picks on my tablet, but you should of just raised the multiplier and the Vcore volts to get the overclock.
1.3 sounds a bit high I would start at 1.28

 

[c4su4lty]

I've been looking through all of the options but I can't find a menu to increase NB Voltage.
There is also none at "Advanced - Northbridge Configuration" .

 

[c4su4lty]

I figured it out myself.
Setting LLC to 5 and Offset Voltage from -0.03V to +0.01V made it stable.