Strange Internet connection problem.

i have an unusual problem with my 16 month old Inspiron 1501 laptop. It suddenly will not connect to the internet. It says that it is connected to my wireless network and that the signal strength is "excellent" however every website says "failed to connect" when i open them, and it does it on internet explorer and mozilla firefox. It has the same problem on 3 different wireless networks i use regularly, and on each of those 3 networks, other computers are working fine, like this one. I have made sure that my browsers are not set to "work offline" mode and they are not. I also tried plugging the Inspiron 1501 into my router directly and it said that connection was good too, but still, no internet. I am at a loss. Any ideas or suggestions?