Fuel Pump Won't Start

I have a 99 Honda Civic Si. It sat for quite awhile while I was out of the country I would say a good month or two and now when I got back I found out that the car would not start. I started checking around and found out that the fuel pump isn't priming itself and there is no fuel pressure. I then proceeded to change the fuel pump. That did nothing. I changed the main relay under the dash that controls ignition and the fuel pump and that did nothing as well. However when I ran constant power to the fuel pump it fires right up. When I ground out the main relay the pump fires again. I am thinking that it might be my ECU. Any thoughts?