I had problems with random freezes and it turned out to be related to the power draw. You can try using the same PSU for the GPUs and their associated risers to it. If it does not help, I'd go with checking all the cables and using treanski's advice.
never use fucking sata i already said it...not with adapters not any other way, only 4pin or 6pin molex
since i stopped using sata for powering risers 99% of my problems are gone
Getting rid of random freezes is a real pain, took me two days going step by step to rule out possible problems.
I think you may be on to something with the power aspect.
So last night I swapped out all my risers and changed virtual memory to 16gb. I started mining and went to sleep. I woke up and the machine was frozen up again. The 1070 ti Zotac AMP EXTREME cards require two 8 pin connections, so I was forced to buy these adapters:
https://www.amazon.com/gp/product/B07611QXG4/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1I ran those adapters for 4 cards. I unplugged all four of those cards and just ran the two cards that I am running without adapters, nearly 9 hours of up time so far. It has not locked up today. I think 1 or more of those splitters might be bad.