Gtx 780 Phantom not working

Oct 7, 2018
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I just bought an Gainward gtx 780 phantom,and I use an aero cool integrator 500W 80+ bronze PSU.
The PSU have's only one 6+2 Pci e plug,and the card needs an 8 and 6 pin connector to power.
I bought and 2 molex to 6 pin connector,and after installation,the card fans start at full speed,and the monitor is all black,if I disconnect one of the plugs,i get "please power down and connect the Pci e power cables for this graphics card" message.
My pc specs are:
Msi FM2 A55M E33 mobo
Amd a8 6600K procesor
WD blue 500GB HDD
8 GB DDR3 1600 mhz ram.