Music and movie files won't play in Finder using macOS High Sierra

No error messages, just no response when I select the play icon for a compatible music or vidoe file. To expound, when in Finder, I navigate to and select a file, such as a .mp4 or .mov file for example. In the Finder preview pane, I click the play icon for the selected file; but, instead of the file starting playback (as it did in previous OS versions), nothing happens. One anomaly I have noticed is after clicking the play icon of the selected file and then switch to a different folder still within Finder, the previously selected audio or video file will start to play in the background. If I then navigate back to that audio or video file that’s playing in the background, the playback stops. That’s pretty much it. Hopefully this makes some sense. I’m currently replying on my iPad. Once back on my desktop, I can send screenshots if that would help.

I had not before, so I just tried it...doing so (i.e., pressing the "spacebar") opened up a pop-up window and I was able to play/view the selected file. This technique is not what I'm used to, but I actually like it way better than what I was doing before. Thank you for the advice. I did not know about this technique until you bought it to my attention. Thanks again.