Copy and Paste [branched from original thread]

Hi @Kevin-Monahan, another question. I don't know what happened with my Premiere Pro. Still, every time I copy a video or audio and paste it on the timeline, it just pastes on any of the timelines and usually replaces all the things I've already done. It just destroys my timeline so what I do is lock the timeline so it will not affect all that I already put in place. Thanks!