Questions:

What's your RAM and Virtual memory?

I think you have a few problems.

My guess is that you shouldn't have three separate PSUs as this can trip the mobo. That and the power you have doesn't sound like you have enough power. I have 4/5 GPU's to 1200W normally to be on the safe side.

And there may be an issue with your GPUs because you have both NVIDIA and AMD GPUs which are completely different. Not saying that they won't work together but they can cause issues.