Okay, for starters, look at your keyboard. Find the capslock key. Make sure the little light is OFF.
If you want help, please take the time to describe your problem in more detail. If your computer is not starting, it could be a number of things... it could be your CPU, your motherboard, your power supply, your hard drive, even the power switch on your case.
Be specific--what happens when you press the power button? Does it power up at all? Does anything appear on the screen? What kinds of noises does it make?