Running Integrated and Dedicated Graphics At The Same Time

Hey all, I know this question has been asked before, but I haven't found an answer particularly pertaining to my situation. 

First of all, I have an HP Compaq Elite 8300 with an Intel i5-3470, integrated graphics (DisplayPort and VGA.) I also have a dedicated GPU (Nvidia GeForce 7300 LE.) I enabled the integrated graphics in the BIOS to use both the integrated graphics and the dedicated graphics at the same time. 

Now, I have one monitor plugged into the integrated graphics, as I set that as the primary GPU. Whenever I plug a monitor into the 7300, both screens go blank and nothing shows up. As a matter of fact, on start-up once, I had all four monitors plugged in and all that happened was that every monitor stayed blank and blinked every few seconds. Any ideas on what to do?