When my computer is turned on the monitor green light comes on and the keyboard blinks, for a second then turns yellow and the keyboard doesn't work. This is the same problem I had before building a new system. I have a new power supply, motherboard, memory, processor and case.

Well then, the problem is not likely one of those components (what about video card, monitor, keyboard?), or your build technique is flawed (for example, failing to use thermal compound between the processor and its heat sink), or an environmental condition (bad utility power).

Is anything displayed on the screen?