Full power but no crank

Okay, so as of the past two weeks I have been experiencing starting issues and had massive power draining, but I had an fairly new one year warranty battery in it and low cranking amps. So I figured maybe that was part of it along with possible radio draining it too because I had noticed it was on when turning the key. Replaced the battery with a five year warranty battery from Wal-Mart 76N with side posts. Had it installed by them and everything was done, with a new high mileage oil change. Fired up like new and drove around fine. Couple days later I decided to leave the house and it would not crank over but had plenty of power going to everything. No crank, no noise except the door ajar noise. Checked my fuses on the inside of car and replaced one of them (lighter socket). I am hoping it is a starter issue and nothing else. Also, it has a service light on now, so maybe that is a related issue?