Only connect one display to the non-working port. Boot up. A good card will detect and you'll see the BIOS and Windows boot up. If not, then try another card. Could be an odd cable issue but details are rather slim.
So, I've spent the good part of two hours trawling the internet and I can't seem to find any fix for this problem.
I'm running Windows XP, have just set up a dual-monitor system (Acer AL1916 and Acer AL1906). I have two ports at the back of my computer, a VGA and a DVI- the primary monitor is attached to the VGA port, whilst the secondary is attached to the DVI via a VGA-DVI adaptor. My computer is recognising the second monitor- it's letting me have a dual-screen set-up, the mouse moves between monitors etc, but the secondary monitor is blank and coming up with the 'no signal' message.
So, it's obviously connected as the computer's recognising it, but not connected to the extent that it's sending a signal. I tried switching over the monitors (plugging the secondary monitor into the VGA slot, and then plugging the primary one into the DVI adaptor), and the secondary monitor worked but the primary one hasn't- so I figure it's nothing to do with the monitor screen being broken.
I've tried driver updates, setting changes, Windows updates, and I'm starting to get to the end of my tether- any ideas at all? Cheers!