My dell latitude d610 laptop won't turn on?

my laptop won't turn on. now i am using it. Whenever i shut it down, then turn it on again when i forget to do something, it won't turn on. It will take another time to turn it on, like for example i leaved it for 3 hours then there it works again, and after turning it to off, then leaved it for 3 hours, there it won't turn on again. It turns on whenever I am lucky that the laptop will turn on. Here is what happens, When i press the power on, the power icon just lights for 3 seconds and off. You could not see the caps lock icon or num lock icon turn on, just the power on. please help. DELL!!