It says 'forbidden your client is not allowed to

Hi there,

Please check if your browser using proxy settings, If so try to go to the normal mode.

the link for youtube is : http://www.youtube.com/

Still problems, try with another browser like Firefox Portable, I use it right now :
http://portableapps.com/apps/internet/firefox_portable

The good with this one is that you just have to delete the folder where it is and vupti the program is gone :0)

You may need additional Adobe flash player for firefox for see youtube movies, you can get it from here:
https://addons.mozilla.org/en-US/firefox/browse/type:7

Hope that helps
IF NOT then try to return here and tell me which browser you use
Have a nice day

Please rate my answer