You choose from one of the two or three connections.
And the DVI port would have to be one that has VGA signals. Many DVI ports are strictly digital.
The lack of details means I can't tell you where it went wrong but try the DVI to HDMI next since that conversion usually works every time.
I have a ASUS AMD RADEON 6450 graphics card and im trying to set up dual monitors yet my computer fails to detect a second monitor
My primary monitor is plugged into the VGA slot whilst my second is connected to the DVI slot using a vga cable and a vga to dvi converter i purchased from amazon: http://www.amazon.co.uk/dp/B000FII81...005151_3p_dp_1
my pc only seems to recognise output from my vga port and not from my dvi nor hdmi port