Hello fema,
I had the same issue with my Gigabyte Z97X-UD5H, I flashed the newest BIOS (F8) and my PC was working fine. After two weeks I reinstalled OS and now I am facing the same problem again...
My specs:
Gigabyte Z97X-UD5H
Intel i7-4790K
4x4 GB RAM Corsair XMS3 (set in BIOS to XMP profile 1600)
MSI Geforce GTX 760 2GB
PSU Seasonic G 450W
SSD Samsung 840 Pro 256 GB
3x HDD Caviar Black 2TB
Adaptec 6405 RAID controller (3x HDD RAID 5)
OS: Windows 7 Ultimate 64bit
As I already mentioned, I had the same problem and tried following: I removed graphics card (turned the CPU graphics on), removed Adaptec controller and disconnected all HDDs. After booting Windows, my PC rebooted everytime, when I started any task, which needs "a bit more" CPU. For example I was not able to run the Windows Experience Assesment - my PC shut off at the "CPU task" and started again.
After several days trying I flashed the new BIOS version to F8 (the MoBo came equipped with F6) and then worked everything fine. But my PC was so often restarted, that not only the file system, but also the installed software was corrupted. I decided to install new fresh copy of Windows.
You can guess, what happened. I am facing the same problem AGAIN. I flashed the F8 again, loaded default values in BIOS, removed and disconnected hardware as before, but no success.
I installed HWMonitor to check the CPU temperatures. Before upgrading BIOS I have seen temperatures above 90C, which is abnormally high. I touched the heatpipes of CPU cooler and I can swear, they were not that hot. I was thinking about bad placed cooler or missing thermal grease. But everything was ok. I have not seen any high temperature after BIOS upgrade, I think I have seen max. 70C at full load. I thought, the old BIOS version has an issue on how to read or interpret CPU temperature values and CPU (or motherboard) turned the PC off, to protect CPU from frying.
But now, running BIOS F8 with fresh Windows installation, shows the HWMonitor temperatures about 30C at idle but if is there any need of CPU, then PC shuts down immediately.
I tried also to remove CMOS battery for 1 minute with disconnected AC, followed by loading default values in BIOS with no success.
I'm not sure if I'm experiencing a hardware or software (driver?) issue.
Any help or advice is welcome.