I have a 2001 Ford Focus ZX3. Last week I left the lights on while at work so they battery died. I took it to Wal-Mart for a recharge and when I reinstalled it in my car the car didn't even try to turn over. I was hearing a sound that sounded like a small electrical engine humming so I opened the hood and thought the sound was coming from the starter relay. I replaced the the relay but the car still doesn't turn over. Anybody have any advice for what I should do? I figured I should check the starter to make sure it worked but could it be something else?