psu won't boot up, pci-x issue

[boasist]

so i picked up a molex-pci-x converter for my 7800, before i was using the card with no power, not playing any games, just setting the system up. not i connect the 2 molex plugs to molexes' on different cables, plug in the pci plug, and it doesn't boot, not anything, removing the pci-x plug makes the system function normally. Can i operate this pc with my current setup?

fx-55
msi r480
7800gtx oc
1gb g.skill
cd-rw
zalman cpu fan

using a seasonic 400w 24-pin psu.

i've tried my only 2 psu's an antec 350 and the seasonic 400 neither work in this situation.