Open Question: Improve video streaming?

Ever since i got this new modem (Wireless-N 300 Router with DSL Modem) videos and some websites have been loading slow or not at all when the modem is supposed to be able to stream HD videos while surfing the internet, make internet phone calls, and play online games. some youtube videos won't even start to load and will just come up with some error message. also, itunes has been messing up lately saying it can't connect to my ipod or something. i never really had this problem before. please help if you can.