Can a 770 run 144hz?
yes a gtx 770 can handle a 144hz display with or without G-sync. though to get 144 fps/hz you will have to turn your game settings way down if it is possible at all ( i had a 144hz display once upon a time usually the CPU can’t crank out the frames to the GPU fast enough but in gpu constrained games it is reversed).
How do I hook up my GTX 770?
Most 770’s use one six pin and one 8 pin. Choose any two of the PCI-e lines, install the gpu in the uppermost pci-e lane (closest to cpu), plug in one line use both the six pin plus the two pin into the 8 pin connector, and plug just the 6 pin portion of the second line into the 6 pin connector.