A little more information maybe helpful. When you say that you push the button on the cpu it doesn't start; what do you mean? Do any fans spin? Do any lights come on and then go off? Is this a new computer that you have just build?
Just so you know PSU (Power Supply Units) are one of the most common things to go bad so you always want to start there and see if you replace that if it will get the system back up and running. After that we can try to help you out with a little additional information.
Do you have RAM installed, and is there anything metal touching your motherboard, ie. the i/o shield or even bolts from and aftermarket CPU fan could be touching bare motherboard material and not letting it post. This happened with me on one of my water cooled builds where the CPU/PSU were not turning on to prevent a short. So i made sure there i used some plastic washers to ground off the metal and voila, it worked.