When trying to import a small 37MB video, the import dialog pops up,you choose where from/where to/etc. but then Lightroom just stays and gets hung on "Importing files" including the progress bar in the top left corner hanging/not moving.
We use these little videos for GIFs we make otherwise we'd store these elsewhere of course.
Does restarting your computer fix this? There's a flakey component of LR that handles video, and it can be "fixed" by restarting the computer.
If restarting doesn't help, attach the video to your reply here, and we can see if this is specific to your installation or occurs on all installations. That will help narrow down the problem and perhaps provide a reproducible test case to Adobe.