Bluescreens after upgrade

[Just_a_question]

Model of Motherboard: Asrock P55 Extreme4 (BIOS 1.5)
Model of Memory: F3-10666CL9S-2GBNS
Model of CPU: i7 K875 @ 2.93 GHz
Windows 7 (64 bit)

I had 3 x ram and then decided to buy a fourth one (all of them of the type mentioned above). [The reason was the mobo manual says I needed either two or four rams for enabling dual channeling.] Since I bought the fourth ram I occasionally get blue screens, and windows tells me there are hardware ram faults.

I removed the new ram, and the system worked fine again. Then I removed one of the old rams and replaced it with the new one, and the system worked fine as well. So it seems the problem only occurs when all four slots are in use - regardless which rams I use.

Dows that mean the fourth slot is faulty?
Any idea how I can solve that problem?

(I'm kind of a computer noob)

Thank you so much!

[Tradesman]

Could be a slot, could also be the timings and/or voltage. Could you post you BIOS Settings

[Just_a_question]

This is set manually:

667 MHz DDR3 - 1333
DRAM Voltage 1.500 V

The rest is set automatically:

tCL = 9
tRCD = 9
tRP = 9
tRAS = 24
tRFC = 74
tWR = 10
tWTR = 5
tRRD = 4
tRTR = 5
tFAW = 20
CHA RTL = 54
CHB RTL = 55
tWL = 7
RttNom = 20
RttWr = 120
PD Exit Mode = Fast
B2B CAS Delay = Disabled
Command Rate = Auto
Enhanced Training = Auto

[Tradesman]

Might try raising tRFC to about 82, manually set Command Rate to 2, and/or raise DRAM voltage to 1.55

[Just_a_question]

Hi Tradesman, thanks for your suggestion!

I wasn't able to change tRFC (it's grayed out), but I set Command Rate to 2 and raised the voltage to 1.55 Volt. Now I'll wait if any further errors occur. I will let you know what happens

Again: Thanks!

[Tradesman]

What you've done may well be all you need, if CR defaulted to 1, that well could have been the problem

[Just_a_question]

Thanks again for your suggestion; my system is much more stable now: There were "just" two blue screens during the last weeks. That's much better - but not completely satisfying.

Is there anything else I can try?

edit: the last blue screen said: "Page Fault in Nonpaged Area"

[GSKILL TECH]

Memtest the memory to confirm they are error free. This memory should be plug and play.

Thank you
GSKILL TECH