PC shutting down only in GTAV and RDR2

Hi, I'm facing a peculiar issue. My PC randomly shuts down, but this only happens when I'm playing GTA V or RDR 2. I'm baffled about the cause since it only occurs with these two titles. I've played many other games, including newer ones, without this issue arising. Interestingly, even when running FurMark, this problem doesn't occur. A year ago, I attempted to install two discrete GPUs in this PC (adding my old gtx 650), and that's when this issue first appeared. However, removing the second card didn't resolve the problem. Does anyone know if this could be related to an incorrectly connected cable to the PSU, or perhaps connected in the wrong order?

My specs are:

GPU: GTX 980

CPU: i7 4790k

Ram: 16gb DDR3 1600mhz (three slots)