what do you mean by rail? see im not a smart man when it comes to the hardware side of these things as you can see. I thought you just plug it in to the PCIe x16 port and it would be all peaches and cream.
Some power supplies are split into two rails, so roughly half of the power is distributed on each rail. You may have a single-rail model so I wouldn't worry about it too much, but if it still doesn't work after you plug it in, than try using another 6 pin connector.
Can you post some information on your PSU?