Computer Died and wont boot up!

I just built a computer with a Core 2 Quad Q6600, 2GB of ram, 500 GB sata hard drive, PNY GeForce 8800 GTS and a cheap 800 watt power supply (less than $100 canadian). I had just installed the operating system and was installing drivers, when all of a sudden all power was gone. The PC didnt crash (could tell by the noise) but just lost 100% of power in a spit second. Now when I try to start it again Nothing shows up on the screen (no bios, and no blip). This same thing (black screen) happened when I forgot to put an extra plug from the power supply to the motherboard for extra graphics card power. Dont know if this helps. Also all the fans turn on as well as the light on the motherboard. What part will I have to exchange on this brand new PC!