I beleive there is a 4-pin Molex hard drive power dongle on the video card (eVGA GEFORCE 6800 GT DDR3 256MB DDR 256-bit AGP8X). Maybe you missed connecting a power feed to it when you installed the new PSU? I know you said you checked to make sure it was well seated but you did not say anything about this power connector. I went EVGA's site and the best match to your model may have this extra power connection. I hope this helps.
OK..long tale . This morning my son's PC just didnt turn on... soft button..nothing. Hard switch on back .. still nothing. Then it kind of started but chug-reved like a bad car starting... we decided to check the power supply... Put a brand new 600 watt in. Now it starts up, pretty lights =P, but the monitor isn't getting a feed... I don't know if I connected some wires wrong or even what to check.
But I did check the video card (eVGA GEFORCE 6800 GT DDR3 256MB DDR 256-bit AGP8X) to be sure it is seated and connected to the power. Am I missing something obvious? I know there were a LOT of wires to connect. He has 2 dvd drives and the hard drive.
I am wondering if it's even booting but since I can't see the monitor I have no way to tell. How can I be sure the HD is connected right? Should there be any sound (like beeps) when it's starting?
The mobo is Gigabyte GA-K8NS Ultra-939 nForce3 250Ultra
Hard drive is Western Digital Caviar SE 160GB Hard Drive
Anything else you need to know..just ask