molex to pci-e connectors arent always the best. if the psu doesnt have its own 6 pin connector, then it probably originally wasn't design to run higher end gpus with 6 pins on them. the molex to 6 pin is generally aimed at units that only have one 6 pin connector, with a low end card that has 2 6 pin connector slots(psus with 1 6 pin connector that can handle stuff for example is the antec earthwatts green 430w, which probably had 1 6 pin to cut cost.)
the psu does has a 6 pin connector i plugged that in now and still no display, there is a driver disk that came with my the 550 ti, do i need to install that? but how if i don't have anything to look at.