Computer Doesn't Boot when I add a second power supply

[4Bondz]

I am building an 8 card 1060 mining rig. I have booted the PC using a 750W power supply and am running a prime H270-Pro board with 8 GB of DDR4 RAM and 2 1060 3GB graphics cards connected to the board on risers.
I have 6 other cards being run off of a 1200W Thermaltake PSU and while the PSU can power up the cards, whenever I plug any one or more of the 6 cards not being powered by the 750W PSU into the motherboard, the 750W PSU clicks on then instantly clicks off and refuses to turn on again unless I shut it down completely and turn the switch back on. Is there a reason that this would be happening?

Thanks

 

[mdd1963]

GPUs also draw ~60 watts or so from the PCI-e slot they are plugged into....; run the motherboard's 24 pin ATX power and 5 GPUs from the 1200 watt PSU, and the remainder from the 750

There is also no certainty that your MB will function with 8 GPUs plugged in due to PCI-e lane limitations....