Ubuntu 15.10, Nvidia CUDA: 970 GTX combined with 950 GTX is not working

I have 2 GPUs, a 4gb geforce gtx 970 and a 2gb geforce gtx 950 and an 800 watt powersupply (using the brand new 4 core i7).

I am ruing using CUDA drivers, and I would like to have both cards installed on the motherboard so that I can use one device to run my code, and the other GPU for development and debugging.

I just installed both cards at once and booted up; did not get a single monitor display through any of the VGA/DVI/HDMI ports--not even a BIOS screen or safe mode prompt.

How do I go about getting the second card installed? Do I have to set my current GPU as the primary display GPU somehow?

...Right now, I took the 950 out and am ruing with the 970 on the motherboard.