Based on the tests done by you so far, I'd next recommend the following as a hint towards narrowing down the cause:
1. Restart the system into BIOS, clear the event log and load the BIOS default settings.
2. Otherwise, ensure the power supply is the power supply is 460 W., as minimum.
3. If the problem continues, see to it that the memory modules are not above 1.55v.,as the CPU itself is not tolerant to higher than 1.5v.; see the following URL: