I have got a GTX 970 connected with 3 monitors, this works perfectly with the nvidia 343.22 drivers.
When I connect a fourth monitor with an active DP → Dvi adapter http://www.sapphiretech.com/presentation/product/product_index.aspx?pid=357&lid=1 all monitors turn black and they don’t receive any input. After a reboot the screen turn black after GRUB. When I remove the DP → DVI adapter and reboot the pc the 3 monitors work perfectly again.
In Windows the DP-> DVI adapter works perfectly and all 4 monitors also work. This is with driver version 344.48.
I already reinstalled Ubuntu twice and reconfigured x many times but 4 monitors connected to the card in Ubuntu 14.04 and 14.10 still doesn´t work. I am thinking this is a linux driver issue because in Windows it works. Do I actually need an active adapter or will a passive one also work and maybe fix the problem?