PCI-e no power on

[[t..o..m]]

I recently purchased a MSI NX8600GTS 512meg HEATPIPE COOLING, 2GB DDR2 800MHz RAM, E8200 CORE 2 DUO CPU, and a ASUS P5N-E SLi nForce 650i all brand new. It all powers on ok, but the monitor just displays black with a ‘no signal’ message on the screen. No system beeps, no POST test, just black screen. (monitor is a 22")

I’m using an older style power supply but it still has 550W. I’m wondering whether the PCI-E card isn’t getting enough power? Do I need to buy a newer PSU which supports PCI-E cards via some special power connector? Is the power supply powerful enough?
The power connector to the video card is the same as a 4 pin normal molex cable.

I was using the molex cable to power on my video card but it obviously needs something more powerful… Help?