orange light blinking on motherboard, wont turn on.

I just recently got a computer that wont boot and i took it apart and put it back together and it still wont turn on. i think the power supply is fine but im getting an orange blinking light on the motherboard that is right next to where i plug in the hard drive. what do i do to get this thing working? im not that educated on the physical side of computers and im having a hard time finding a solid answer. thankyou.