4th Monitor not recognised

I have had 3 monitors connected for years and finally connected a fourth. Windows (8) will sort of detect it but not completely.
In where I change appearance of displays 1,2,3 are detected. 4 has a little window saying "display not detected", but it is in fact detected or that little window saying "display not detected" would not be there.
2 Monitors (1 and 2) are off the motherboard, 3 and 4 are off a pci card.
The one that does not work is connected to the DVI port on the card.
I have re installed the pci video card software again, but makes no difference
Suggestions please

Post the make and model of the video card you are using. I did not see it in your signature.

It is a power color pci card with amd radeon 4300 grahics

I reinstalled the software and finally got the monitor recongised, see the attached pic.
Number 3 screen
Problem now is there is nothing on it, just a black screen.Attachment 10881

Does the monitor have a DVI port/cable that you are using to connect it to the card, or are you using a DVI to VGA adapter.

The monitor is agp connected to an adapter on the dvi port

If one of your monitors has a DVI connection and cable, try that one on the DVI port. If it works, then the adapter may be the problem.