Youtude

If there is something wrong with your device or settings, that can effect the ability to view content on YouTube.
Try enabling or disabling Adobe Flash in your Browser/Settings/Display and Actions or try enabling Desk Top Mode in the Browser/Settings/Developer Tools.

Some YouTube videos are flagged to not be viewable on a mobile device, that is a flag set by the uploader or YouTube, in some cases.
Some are region restricted by the uploader or YouTube, viewable if you are in one country but not in another, you can use a proxy service to get around that.
Lastly, some regions or countries believe their citizens do not have the right to view some content on the internet and block access to that content. Sometimes a proxy or tunneling service can bypass that.