Maybe one of the core is bad. Same case with mine too. When priming the first core will always fail first. Raising Vcore is one of the options but my E2140 is not reacting well with voltage. At 3.0Ghz even 1.45V causes reboot when priming. Yamcha, I think you RAM can go till 400mhz. Try raising the voltage to 2.0V and loosen the timings too 6-6-6-20. My previous PC5300 can do 400mhz at 1.9V 5-5-5-15.