CPU fan not spinning

I have just built a new PC. I have a asus H81M-E motherboard, 4GB RAM, intel G3240 3.1 GHZ CPU and GeForce GTX 650 graphics card and a 500W power supply. When I turn the computer on the CPU and graphics card fans start to spin then stop and the computer powers off and after 1 second powers back on but the fans still do not spin. I also have no video signal from my PC. Please help!