Just making sure, is the 750ti the 'Zotac GTX 750 ti 2GB OC' with two fans. That version does have a 6 pin power connector that must be plugged in.
The plain single fan Zotac GTX 750ti with 1Gb has no connector and uses power from the slot.
If you have the 2GB OC, top section of the card, furthest away from the video connectors, rectangular black plug, 6 holes.