Can you give a little more info? What exactly did you do to overclock? What did you change? FSB? Ratios? Did you unlock the 4th core?
FSB - you might need to raise NB voltage or it could be that the RAM is now too OCed and you need to either lower RAM ratio or increase RAM timings
Unlocked core - might be unusable
I raised the FSB to 224 which is stable but not above (set to async with PCIe) and unlocked a 4th core and L3 cache. Its not the RAM I lowered the multiplier and even tried it as low as it would go. I didn't try the NB voltage though. If I raise the core voltage above 1.4V its no longer stable even at the 3.35GHz.