I did a quick Google search and the few post I looked at either had no answers or suggested that the problem is the display port to DVI adapter must be an active adapter for the 3rd monitor to work.

The installer installed the basic AMD drivers and then pulled updates from AMD giving me the same AMD drivers as I had downloaded originally. Then I went to HP's driver site and downloaded their AMD firepro drivers for the z400 workstation. So I tried this, but when Windows saw the card it only recognized it as a standard VGA card even after a reboot.

I did a quick SW search and saw a question from Jan 2013 where a guy had a similar problem, and according to the post, he got it working by uninstalling the AMD software and drivers and letting Windows pull down the driver. I can use both display port or DVI with 1 display port or the other but not all 3. When I logged into Windows (as a domain admin), Windows and the AMD software can see the 3rd monitor, but it simply won't display on all 3 monitors at once. While the computer boots up, the BIOS and Windows splash screen shows up on both the diplay port to DVI monitors. I grabbed the latest drivers from AMD and installed the card. The Firepro has 1 DVI port and 2 display ports, and it came with 1 display port to DVI adapter (according to Newegg it is an active adapter but according to a post on an AMD forum, it ships with a passive adapter) so I purchased a second display port to DVI adapter (Newegg didn't say if it was active or passive). I was asked to try to stay under $400 per card, so I got the AMD Firepro v4900 specifically because the datasheet said it supported 3 monitors. So for the user which has 2 monitors, I bought an nVidia Quadros K600 and it seems to working ok. The other user has 3 monitors (all DVI input). They both have the same computer (HP z400 workstation with Xenon processor, 10 GB RAM, and 1 TB HDD running Win 7 pro 64bit).

I was asked to research a replacement video card for our 2 CAD users.

Amd firepro w4100 no signal