Question PC won't start after new graphics card installed ?

[Cervical]

i recently acquired 3 x GTX 980 cards. They all work in my other pc but when i install them in the problematic pc it won't turn on when I connect the PCIe cables.
I've searched for solutions and have found none that have solved the problem, anyone have any ideas?
The spec of pc is in the linked

 

[DSzymborski]

i recently acquired 3 gtx 980s they all work in my other pc but when i install them in the problematic pc it wont turn on when i plug the pci-e cables /. ive searched for solutions and have found none that have solved the problem anyone have any ideas?
the spec of pc is in the linked

The best place to start, for anyone to have any ideas, would be the full specs of the problematic PC, including exact power supply. Hard to diagnose a problem with a PC that's a complete and utter mystery.

 

[Cervical]

eclipse sli ms-7520 mb and i7 970 chip ....8 gig ddr3 ....has 3 pci-e slots ......pc ran rx570 no issues and my other pc had no problem with the 3 gtx 980 they work fine in it

and i powered with 2 seperate 6 pin cables
sorry i have a seasonic x560 80 gold powering the pc

 

[John Chesterfield]

You failed to specify power supply..

 

[DSzymborski]

Yup, the power supply is the most important bit of information.

Junky power supply is one option. The apparent lack of UEFI on this motherboard is another; getting Nvidia GPUs after the 700 series to work is really hit and miss.