Youtube won't play blocked plug-in????
What is blocked plug-in????
MacBook, iOS 8.0.2
That usually means Adobe Flash is being blocked. Some Youtube only requires HTML5. Click2Flash is a utility that frequently blocks Flash for some. No MacBook can run iOS 8, or Classic Mac OS 9. Apple's iOS will not run Flash, although HTML5 based Youtube videos will play on iOS.
Depending on what you are running, you will need to post in the right forum to more succinctly define what your problem is: