03 focus just won't start

My 03 Focus will not start. I hear the click, click noise of the starter but nothing else. The lights and stero comes on but that's about it. It did this yesterday morning but started right up by the afternoon with nothing done to it. Can someone help me with this.

If the battery hasn't been replaced since the car was new (5 years) it probably is on the way out. Most parts places will check it for free. If you want to check it yourself with a voltmeter it should register 12.8 with the engine off.