2000 Mercury Marquis fails to start at times

I aquired this car from my dad after his passing. It sat in the garage for several mo. I would start it occasionally. Low battery charge at times would not start. Charge battery it would start. At times the fuel pump would not activate at the turn of ingnition switch. Play with it for a while and fuel pump would hum and it would start. Let it sit in the garage for a while longer. Same thing would happen. Checked fuses and fuel pump relays. Let it sit and it would start hours later. Decided to drive it home last week. I listened for the fuel pump at the turn of the key. Didn't hear it at first. Then I did hear it and it started. I brought and installed a new battery since the car had sat most of its life. Car started and headed for home. The car ran great. I stopped 45 mins. Later at a Murrays to buy new wipers. The car would not start. I did not hear the fuel pump ativate. I tried replacing the fuel pump relays. No luck. I let the car sit for hours. It still would not start. Tried to use a computer to check for trouble code. No code showed up. I towed the car home. I am ready for the next step. I am ready to drop the tank and replace the fuel pump but don't want to spend the $ if I should be trying other things first. I though about checking the voltage to the pump when the ignition key is turned but I have done it yet.