Newly built computer, can't get it to turn on..

I just built my own pc and for some reason or another I can't get it to turn on. These are the components I used: The case is a XION axp 100 series with a recommended 700w power supply, an Intel Pentium 4 D915GAV motherboard,I installed the recommended 2 gigs of DDR400 memory sticks and are placed in the right DIM sockets. I wired everything up according to the diagram, the motherboard is powered by the 24 pin connector as well as the 4 pin connector, the hard drive is powered by the sata power cable and connected to the board by the second sata cable. Now when I turn on the switch on the back of the power supply the LED light goes on the motherboard,but when I hit the power button on the case nothing happens, not even the fans go on. I took it all apart and rewired everything again and still the same problem occurs. Does anyone have a solution to this problem???