Pro Input needed

[NC37]

Trying to isolate some issues on a friend's rig that I built for him about a year ago.

Starters his specs are roughly:

Phenom II X4 955BE @ 4Ghz (currently, had him clocked down to 3.6Ghz for awhile)
890GX AM3 Gigabyte board
8GB 1333 RAM
Radeon 6870 1GB
Win 7 Pro 64bit

He's had random BSODs. Can't replicate them. Just something that happens. Originally I had him at 3.8Ghz on the initial build. Issues cropped up so I clocked it down to 3.6Ghz. Issues that could be replicated went away. Applied some more insight recently, clocked it up to 4Ghz bit by bit, CPU core to 1.45V. Then gave it a little more voltage on the CPU-NB along with taking the NB freq up to 2.6Ghz. Tweaking the NB was what I didn't do before and seems to have helped get it stable. Similar what I did with my setup after I read up on it.

Now heres where the questions come in. Ran Prime, 2 cores running fine. 3rd Core lags a bit but finishes. But then the last core just seems to hang there. Other cores finish multiple tests and it still remains stuck on test 1. Found people using Vista noted this issue at times but he's on Win 7. This doesn't happen on my older system. The cores finish are roughly the same time with maybe one lagging slightly but not much.

Then I ran Cinebench and noticed one core lagging quite a bit behind the others. Test results at the end gave it a 3.14 rating. This rating is worse than my old nForce 570 AM2. Right now I'm hitting a 3.78-3.92 range @ 3.45Ghz on my 945 (depends on my NB freq) with 4.04 at 3.6 Ghz, but speed is not stable.

I'm wondering, could one of the issues all this time been a defective core? Or something else?

 

[Peter1986C]

According to the specs, it is rated at 3.2 GHz so it is overclocked. I suggest putting all frequencies at stock ratings, including (but not limited to) the cpu, NB, ram. Do the same with all voltages, including (but not limited to) PLL and VTT voltages, ram and cpu voltage.
BTW, the memory controller is in the cpu with that cpu model, the NB is not involved with the RAM, AFAIK. But I suppose you wrote "NB" because the BIOS refers to the IMC that way.
Please note that RAM branded as Crucial and OCZ may need a manual set-up of the voltage, clock speeds and latency values (instead of "auto"). Make sure that "memory remapping" is enabled (if it isn't already) and check the PCI-e frequency (which happened to have jumped up for an unknown reason in case of my pc once). The latter should be at 100 MHz.
Does the graphics card have a custom cooler? If so, then I suggest reapplying thermal paste on the GPU, and reapplication of the VRAM/VRM heatsinks.
I read somewhere that it is better to limit the NB voltage to 1.2 volts, someone here on TPU better verify that if possible.