HELP HELP!! No juice!!

Ok...this may sound silly, but this is the first computer I have ever built. I got a mother board (PC Chips m922lr), standard case, power suppy (ATX 300w), p4 1.6 GHZ, 1GB DDR 3200, floppy, cd drive, 40GB ide 7200 rpm drive, and GeForce4 128mb. I put it all together following the instructions, (have checked, checked, and re-checked) to the letter, but when I turn it on nothing happens...at all...zip, zilch, zero. I dont get so much as a click, beep, or whirl. I know I dont have a large amount of experience, but it did not seem like rocket science to get everthing plugged in and the jumpers set correctly. I guess I was wrong and over shot my abilities.

IN NEED OF ADVICE IN THE WORST WAY!!!

Sara