Only audio is dropped in the timeline

[RyeChusBytes]

I have Premiere Pro 2020. The first video I place in the Timeline goes well. The next videos will only let me place the audio of the video. The visual part can't be placed. 

Help!!!!

[title edited by mod for clarity]

[Ann Bens]

The most common user error is not source patching the track.
Solved by first opening clip in Source Monitor. Then drag/insert into timeline.