After several tries, I discovered a very simple solution for the youtube videos problem:

Just go to this website:
http://www.softwarepatch.com

Search for flash player
and download and install this file. I guess the problem of everybody is because the link on youtube´s website downloads a "non functional file ". this is my personal opinion........

This new .msi file will solve you the problem and you can decide to use IE, or FIREFOX or whatever browser you like! All the programs will work again.