Custom build computer keep rebooting

[ChristmasCC]

Hi! Guys! I built a gaming desktop last year. It runs perfectly until the previous week. It starts rebooting as soon as the Asus logo display on my screen, and it just keeps rebooting. I thought it might be my RAM problem, so I replugged them, and nothing changes. However, I just replugged everything one by one. When I unplug my HDD power cable(I'm using the same SATA power cable for both SSD and HDD), the computer runs perfectly. I replug it; the problem comes out. So, I thought it might be my HDD problem. Then I bought a new one. It still has the same problem. The most wired thing is when I unplug my SATA power cable from my HDD port, it cannot fix the problem. But if I unplug the cable from my PSU port, and replug it, my computer can keep running for a whole day. After that, the problem comes out again. How can i fix it?
System specification:
INTEL I7-6700(non-overclocking)
16GB CORSAIR VENGEANCE
ASUS Z170 PRO GAMING
ASUS STRIX GTX™ 980 Ti
SAMSUNG 850 EVO 256GB
WD BLACK 2TB
CORSAIR RM1000I

 

[Jwpanz]

From the troubleshooting you've conducted it sounds like you've narrowed it down to your PSU as the problem.

 

[ChristmasCC]

From the troubleshooting you've conducted it sounds like you've narrowed it down to your PSU as the problem.

Because I think it looks like a PSU problem, so I narrowed it down to my PSU. However, it seems may not really my PSU problem (no problem without HDD). I just hope someone may has the same problem before who can give me a better answer. Or we can just discuss it.