Graphics Support

Hi, i installed a new graphics card today, i ended up having to clean install the entire system. but the issue i am having now is that on my Geforce GTX750 Ti, i have a HDMI and a DisplayPort port, i have connected my two Dell U2415H monitors via a HDMI cable and A display port to mini display port cable that came with the monitors.

any advice on how to fix that? also when i see what my hardware is in about this mac, it says my graphics card is 0MB despite it being a 2gb graphics card....

Graphics Support