Greeting all

well i just set up a wireless network at home with a tp-link wr641g router and when i connect to it from my Macbook the internet works just fine but i can't connect to my messenger account or to my twitter client also i can't download any podcast from my itunes can someone help me? the connection goes likes this if it helps: Modem to router, router to a Pc, and then i connect to the wireless network,

If anyone can help please do so

thx a lot