flashing amber power button

Help!!! I can not power up my computer. I have a Dell Dimension that is over 3 years old. I didn't change anything but when I came in to use my computer the power button was flashing in an amber colour.  It will not go green and turn the computer on. If I hold the power button for 5 seconds it will turn off completely, but it will not turn back on. When I try to turn it back on, it goes back to flashing amber. I have disconnected the power and reconnected. I have removed the printer and the scanner. I don't know what it means when the power button is flashing nor what to do about it. Please help. I really need to access my computer!!!