It's working now!
After searching on internet I've found a solution.
My MB is a P5B-Plus Vista Edition and after changing the NB voltage to 1.4 and DRAM voltage to 2.1, I can run 4GB Corsair XMS2 in 4-4-4-12 and no post beep errors.
I hope it helps.
Hello,
I'm getting the same problem here too.
I just upgrade my video card to HD 4850 and now I can't keep the overclock in 3.2Ghz. On cold boot I still have the beeps indicating video card problem, but in stock the POST is fine.
Have you find any solution?
Thanks!