It doesn't look like the power supply.
Your Corsair CS650M 650 W PSU got a total maximum power rating on it's 12v rail of 612W (489W @ 80%).
1070ti's maximum power consumption is 180W, multiplied by 3 = 540W (378W @ 70%).

You might be needing a new MotherBoard or SSD.
Problems in the Motherboard produces a lot of symptoms or some slowdown in the system, but overall, it's hard to detect.
What I'm suspecting is your SSD might be failing, freezing and some OS or Program related problems can be a symptom of a failing drive.

Tests you can do so far (one after another):
-Find a Hard Disk Drive for test and trials.
-Try your whole rig in a new Mobo.
-Upgrade to a bigger Power Supply. Preferably, 1000W for your 4 GPU.