My Computer Won't Start

My computer isn't booting up. Everytime i press the button to boot it up it doesn't work. I've check the cables, made sure there was electricity. Recently I've been having this problem but usually it would end up booting up after a few minutes, this time its been over few hours and still hasn't been working. I'm using a Dell E510. During the time when it did work, it would have a green light indicating its booting up but now its blinking orange so I don't know whats happen and would really appreciate any help.