Gam3r01 :
You need to buy a new PSU. If your unit does not have the necessary connections for the hardware you are trying to run, then it obviously is not up to the task of running said hardware.
Just to emphasize this point with a bit of an explanation, your PSU is a Chieftec which is a known very low end poor quality brand. The PSU is rated by them to be 400watts which is the far low end of PSU's that you could run a GTX 960 with. If it was like a Seasonic I'd say you could get away with it (but you really should have a bit more). But being that its a Chieftec, its likely only putting out 350w on a good day. Now there are adaptors out there to add this 6 pin connection, but the problem is you are still under-powering the system. Don't do this.
My motto: if you can afford a graphics card you can afford to buck up for a quality PSU. If you can't then you shouldn't be buying the card.
The EVGA 550 GS or G2 will do the job for you, or the XFX TS 550 or the Seasonic SII 550.