On some occasions due to the slow speed of your internet, it is not possible to watch a video from YouTube with high quality, but you can play a lower quality version easily, yes its .3Gp I am talking about.
Learn How To Download a YouTube Video
Its very easy, you need a web browser, vlc media player and latest versions of flash player installed(no need for chrome users)
Press Alt+p together
Wait and see, the video is playing. Don’t complain about the quality, its .3Gp and its like that!