John has been given some YouTube links that have "https" in their URL, and he can't view them. Leo says that those links are encrypted and Google has been pushing towards https for all video links to prevent hackers from taking advantage of it. Https uses a time-based certificate, and if his computer hasn't been updated or doesn't remember the date, he may not be able to read it because the certificate isn't valid according to the PC. John should check his clock. He should try logging into a different account and see if that changes things. But Leo thinks he's not getting a full page load and that isn't a certificate error. If it's an older computer, that could be the issue. It could also be his internet connection.
The chatroom thinks it's an issue with TCP on his computer. Check out this article by DSL Reports with a TCP Tweaking Tool.