Which CMS are you using to try to display a Tweet? When you visit the Tweet URL in your browser, does the Tweet still exist?
A blank Tweet display is the expected result when the Tweet has been deleted from Twitter.
A typical oEmbed flow will include a HTML blockquote element and a script element in the response. The blockquote displays the text of the Tweet, author information, and a timestamp. The script element returned enhances the blockquote with a full embedded Tweet display.
Assuming your CMS successfully handled fetching the appropriate HTML for the Tweet URL, it’s possible your CMS stripped some or all HTML before outputting the final webpage. View source of the resulting web page (public, not admin) and search for twitter-tweet to find the blockquote HTML element which should be output with the page.