It sounds like you have an inadequate wireless bandwidth to stream video. Can you stream video from other than YouTube?
How many other devices use the wireless connection, how far are you from the wireless radio, what wireless router or AP?
You might also want to check for other interfering networks using the free version of inSSIDer from HERE. Just install it on the machine and run it, look at the networks tab and see what signals are present and if they overlap you and their strength.