It can be many things but every motherboard does that if it's a bad OC. You should start your OC by changing your multiplier to it's lowest setting and then increase the fsb until it crashes. You might need to increase your core voltage. I am not sure what your voltages are now but you will be able to at least increase it by +.15 volts safely without any issues. Do the same thing for your ram as well. Again OCing is different for every setup so it really is just trial and error find the right combination. I usually try to OC a little everyday so it does not get frustrating. The highest I have hit is 4.2 but my temperatures and voltage were way to high for my liking.
A bit down in the page a guys says "try up vcore to 1.475 it will run perfectly. i must say, e6320 is a good cpu, i managed to run it at 3.01 ghz on gigabyte 965p ds3 rev. 1.3 stock HS,vcore at 1.475 , idle between 31-33c full loads 46-48c , orthos 24hours stable."