Graphics card and power supply!

[aashkanaa]

So I have this problem;
When my graphics card is connected to mobo, and power cord (6 pin) is connected to graphics card, all the fans work but system won't boot. (monitor won't turn on). However, when I unplug the 6 pin power cord from graphics card, system boots up but of course graphcis card's fan won't spin. I do have the graphics card show up as AMD Radeon 7660. I also can play games and stuff very well!
Why doesn't system boot when I connect the power cord?
Below is sys info:
AMD A10-5800K 3.8GHz Quad-Core Processor
Gigabyte GA-F2A88XM-D3H Micro ATX FM2+ Motherboard
G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1866 Memory
MSI Radeon R7 260 1GB Video Card
EVGA 500W 80+ Bronze Certified ATX Power Supply
Thanks

 

[clutchc]

Did you remember to move the monitor's video cable from the integrated port to the card's port when the card is installed? As long as the video cable is connected to the integrated ports, the PC will be using the on-board video.