Check your power button . Is it an emachines with a green power button or one of the newer ones with a black power button? Try pulling the face off the computer and check the plastic behind the button. See if something is sticking the button somewhere.
My button is black, it lights up blue,I will check it when I get home tonight. You see when I turn it on, sometimes it will say on for a good while before it starts this, and maybe the next time 2 or 3 mins. or so.