|"With card installed, no signal from the internal mother board VGA socket"|
That's normal since the BIOS automatically disables the iGPU when a PCI/PCIe GPU is detected.
It also proves that you don't have to change anything in the BIOS as the necessary changes have already been made automatically.
It's possible that the existing PSU isn't powerful enough (amps or volts, or both) to drive the GT 710, not unusual on a factory-built PC. It can drive the fans but not the graphics processor itself.
message edited by phil22