Lock cylinder will not go back in

My lock cylinder was hard to get out, but got it out. I bought a new one and the new one goes half way in and not on the way and cannot get to go in. The whole problem was when my gear shift broke on me and I replace it, but when it broke I took the lock cylinder three times and left alone about a week started fix. The first lock cylinder would not turn or come out. I got it out and the second lock cylinder would not go all the way in.