PCIe and onboard VGA conflict

[molenis]

I have a GIGABYTE motherboard with 780G chipset, which also has onboard graphics. My graphics card (HD Radeon 3870) is not booting with the system sometimes. In that case I unplug monitor from HD 3870 (while pc is still working) and plug it into onboard VGA. Then I see system was booted with onboard VGA. Before anyone says, bios is in default setttings (boot PCIe first) and PSU is sufficient (500W Xilence). Thank you for sparing your time

 

[molenis]

Thank you guys, I'm sure you're all very busy

edit: I spotted a used Radeon HD 6850 for 112$ in auction (+free shipment). If my card died, better I know it soon