Insert edits not working here in FCPX 10.4.8

I’ve tried dragging and dropping a video and photo from the browser to the timeline but no insertion area opens and there is no ripple. Instead, either the insert or one or both adjacent clips move to a second row above the existing timeline. When I copy (C) the clip and use W or the insert icon (left side of timeline toolbar), the clip is inserted in the AUDIO part of the timeline, breaking the audio for the duration of the video or photo inserted. I set preferences back to the defaults and this made no difference. Any idea what the problem is and how I might fix it?