Will not start

I have the Elantra model. I replaced the starter and the relay starter fuse and I thought the problem was fixed. I drove the car maybe three times since fixing it and now it is doing the exact same thing. All the dash lights work, the power windows, and the door buzzer/dinger. When you turn the key all the way though it does nothing, makes no sound, just nothing. I got the replaced starter from a salvage yard. Could it be a bad starter? Oh, also there was a stereo put in the car by previous owner that would only work like every other time I drove the car. Could it be frying the starter fuse?