If WordPress cannot embed YouTube video links
One of the most convenient functions of WordPress is that you don’t need much trouble to embed a YouTube video: just paste the link and you are done!
There comes a time though when you discover that a pasted link remains just that, a link, and it won’t be magically transformed into a real video embedded in your page!
Nothing bad happened to your WordPress installation (most probably). The reason why there is no video but only a link, is that the video has been deleted or banned in YouTube!
This means, you need to find an alternative version of the video you need to embed in your page.