I think your problem is your internet speed. But we can test that. I tried to get you to use a chrome plugin to download a video with, but there is a standalone program that is easier. Please download the YouTube Video Downloader
. There is a big green download button on the left side just below the title YouTube Video Downloader
. Once it is downloaded, go ahead and install it and then start it.
Now go to any video on Youtube that you want to watch and try watching it. Once you are done, in the browsers address bar copy the address. Now go to the YouTube video downloader and click on the paste URL
button, then click the download
When it is downloaded there will be a play link in the URL entry. Click on play and let me know if it plays correctly.