I had 2 Titan Blacks and 1 Titan. The system worked fine; after initial problems with Nvidia-driver related black screen which I was able to fix. Today I added a fourth Titan Black (3 ASUS Titan Black and 1 EVGA Titan) (I also upgraded my PSU before adding the new card to a Corsair 1500i, from the 1200. This worked fine).
When I switched on my system I got the following error:
The system is running in low-graphics mode Your screen, graphics card, and input device settings could not be detected correctly. You will need to configure these yourself.
I am using Ubuntu version 14.04.
Update: I restarted the computer and this time the mouse and keyboard weren't recognised/responsive. I then unplugged my usb wifi and restarted again. This time Ubuntu loaded without any problems. Could it be a problem with my PSU?