The restart issue might relate to motherboard BIOS or graphics driver. Please refer to the following instructions for resolve.

1. Update the motherboard BIOS to latest version and Load Optimized default setting.
2. Re-install the graphics card driver to latest version. Driver link: Windows 8.1 64bit ; Windows 10 64bit
3. Make sure the power supply can provide sufficient wattage.
4. Verify the graphics card with other platform.

If problem still remains, please contact your supplier to arrange further examination on the hardware.