If you are absolutely sure you have everything hooked correctly, I would remove the board itself from the case, only hook up the power supply "which may be bad" and jumper the power switch prongs, see if it fires up. If not, it could be a bad motherboard or DOA as we like to call them. This is not uncommon to get a new MB that is bad, it happens with every company and just depends if you were the unlucky one.
So aside from trying another known good PSU with that motherboard, I would say it's time to find your packaging slip and contact for a return.
I am currently working on building my first computer from scratch. I purchased all the necessary components from Newegg, and spent 8 hours last weekend putting them all together. I have been using guides from my motherboard's manual and from a website called kitchentablecomputers. Here are all the parts I am using.
Rosewill Libertas LIB-800 800W ATX12V Power Supply
Antec Nine Hundred Two Black Steel ATX Mid Tower Computer Case
ASUS M4A79XTD EVO AM3 AMD 790X ATX AMD Motherboard
AMD Phenom II X4 925 Deneb 2.8GHz Socket AM3 95W Quad-Core Processor
Western Digital Caviar Blue WD2500AAJS 250GB 7200 RPM SATA 3.0Gb/s Internal Hard Drive
MSI N9400GT Graphics Card
Two older DVD drives, unknown model
Throughout the assembly process, I encountered no confusion with the instructions, it was all quite clear on which connecters went where. Once everything was seated and hooked up, I checked all the wires, made sure they were connected to the right ports, and fired her up. I had a monitor, mouse, and keyboard connected at the time. Upon plugging in the AC power, flipping the on off switch at the back of the power supply, and hitting the power button on the front of the enclosure, something odd happened. There was power, the fans on the case, CPU and graphics card started spinning, the LED's on the case lit up, but only for an instant. Everything then went dead again. It's like there was a momentary pulse of power. I can press the power button again, and the same thing will happen. It repeats everytime I turn the computer on. I don't know what I did wrong, but these results certainly are not right. Another thing; the small LED on the motherboard stays on and green throughout all this. As soon as I turn on the power supply, it will turn on, and stays on until I unplug everything. It seems independent of the main power. I suppose this is encouraging, and that the motherboard has power and has not shorted out or anything drastic like that.
Can anyone give me some advice as to what is happening here? Any ideas would be greatly appreciated. Thank you.