graphics card nvidia sentinal help

[onedestinazn2]

i just installed a 7800gt i got from someone and it had a zalman cooler installed on it. there was only one plug which i supposed goes to the sys power of my ecs 945gct-m/1333. after i turned it on and installed the latest nvidia driver for it, but it says it had to turn down performance due to a lack of power. im currently running a e2200 stock in a antec sonata iii w/earthwatts 500w power supply with nothing else. did i do something wrong

 

[dhc014]

The 6-pin PCI-E power plug on the 7800GT should receive a PCI-E plug directly from the Earthwatts power supply.