3rd monitor problem

I have a Radeon HD 5570 graphics cards. The card has 4 DVI connectors. All of my workstations have no problem with using 3 monitors except one. I've had to reinstall the OS on this box but when I connect two monitors all is well. As soon as I connect the third monitor I lose the second. The special AMD Catalyst Control Center software does not show three monitors connected it only shows one. As soon as I disconnect the third monitor, two monitors reappear and the control center show two monitors connected.

Is this a Window 7 setting that I have to turn on? Is there some kind of AMD setting that I have to turn on? All of the other workstations with three monitors had no problems.

Any help would be greatly appreciated. Thank you.
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Seth SimmonsSr. Systems AdministratorCommented:
found on another forum that it only supports 2 monitors at once; need 2 cards in crossfire to get the 3rd monitor
mfonyAuthor Commented:
I have the same video card in 10 other workstations. All with three monitors.
Maybe the other PC's have an onboard GPU that supports crossfire, and the one on which it doesn't work doesn't, or the onboard video is disabled on that PC?

If that isn't the case, the card could be bad. Test it in another PC which currently works.

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mfonyAuthor Commented:
I can assure you that nobody is doing anything with crossfire. I'm going to test it in another PC (that has 3 monitors) to see if the problem follows the card.
Not sure if this translates from a Mac to a Windows machine, but I have the same problem with my older Mac Pro.  The issue seems to be that the cards are incapable of making all those connection from a power standpoint. To get more than two monitors of work, I had to buy a powered video dongle.  So two monitors will work normally and for the third, I used a Mini Displayport to DVI power dongle. The power comes from a USB connector that is also a part of the dongle. I plugged it into a power USB hub and the third screen worked just fine.

You can buy powered dongles from Apple or I also tested ones from Accell and Kanex.  I think other vendors make them as well.
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