well, buddy its not you only, seems like PTA has inserted another layer in their system from which the address is cencored before going to even the proxy. I am using private proxies and still i can't access youtube.
It seems like proxies won't work anymore, Need to buy a VPN lol!!
PS: you can try http://www.hidemyass.com/ and open youtube from their IP however it may be slower at times.