open it and dust it after removing the battery...blow on it to get rid of static...start it up with battery and power supply plugged in...if still no reaction try looking at the inside of the actual button as this bit usually goes for me (none of my systems are more than 2 yrs old at any given time nowadays...maybe get a cheap upgrade?
It is difficult when you see that way to start a day - you press the power button on your computer and nothing happens. Few computer problems are more frustrating than when your computer won't boot.
There are many reasons why a computer won't turn on and often very few clues about what might be the problem. The only symptom is usually the simple fact that "nothing works" which isn't much to go on.