I cant use my internet even it says connected 2014

Hi. I have macbook pro with os x 10.9.2 software. When i was back in my home country i can use and connect my laptop to any wifi. Now, when i get here to the usa, even if it say my laptop is connected to their wifi, i still cant manage to open a single page when i used safari. The weird part is my iphone and ipad can and easily get connected to their wifi and i can actually use the internet from there. So what is the problem here? Do i need to change something? Please help me.thank you