Help with PC that blackscreens at sporadic intervals

Hey team, so here's the issue. Once in a while my monitor will go black, while the power to the PC stays on (though the fans will audibly shut off/slow down), and no amount of keyboard shortcuts will bring it back. Sometimes the sound will continue, other times it will not. Usually this happens when I'm gaming, but it also can occur when I'm simply browsing or using office programs. Almost everytime it happens I have to leave the PC off for a time. If I reboot immediately then it will crash again within a few minutes time. This has been ongoing for almost 2 years. I recently replaced the video card, so I'm hoping that is not the issue.

Here's my specs;

• Windows 10 Home 64-bit
• Z77-HD3 Gigabyte Mobo
• i5-3570K (x4) CPU
• 16GB RAM
• GTX 970 GPU

Any and all help would be greatly appreciated!!

*Editted for formatting and additional info.