Network Error

My phone is connected to my wireless internet but I keep getting a "Network Error" or "The connection to the server failed" message when I try to go on a website. This started happening after my internet went down and Comcast had to reset it. I am connected to the internet on my Mac and that is working fine. I tried resetting and restarting my phone but that did not help. Comcast said something about authentication but would not tell me more until I agreed to pay them a fee for help. Any suggestions would be appreciated!