I have a Macbook purchased in July 2008. In the last month or so, it has been erratic when connecting to the internet. The Airport Icon at the top of the screen shows a complete and full connection. However, when I attempt to connect to the internet with either Safari or Firefox, it won't necessarily connect. Sometimes it does connect, other times it fails to connect. Either way, the airport icon indicates full signal strength. I am not a strong computer user, so please provide step by step instructions if you have suggestions.