I have a dell dimension. I have a dell dimension 3000 pc that i haven't used for a few weeks as i

Question

I have a dell dimension 3000 pc that i haven't used for a few weeks as i was waiting for an external hard drive to put all my music, videos etc on. I have just come to use the pc and it won't even turn on. I press the button and nothing happens at all. What can I do to fix it??? Please help.... thanks xx