Behaviour described could be one of 4 things as I see it:
1. PSU needing to provide 2x8 12V power like we've talked about,
2. CPU model or revision (stepping) not supported by the BIOS (result: immediately shuts off power). Sometimes BIOS updates (which provide newer microcode) can fix this but only the MB vendor would know. If Gigabyte says that exact model and stepping of CPU is supposed on that board with your BIOS version then you're good, otherwise contact Gigabyte and they might be able to update the BIOS for you (you'd need to send you board to them),
3. Some kind of actual motherboard problem, such as blown caps or faulty VRMs. This sounds extremely unlikely though, as the caps on Gigabyte boards tend to be solid; the first two possibilities are much more likely, and finally,
4. Bad CPU -- extremely unlikely on many levels but is always a possibility to some degree.--
Making life hard for others since 1977.
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