I lose Internet connection after 5 minutes

I have a Dell Inspiron 8600 laptop. When I boot it up I can connect (wireless) to the internet (on IE and Firefox). After ~ 5 minutes, I lose internet capability. The Wireless Network connection will show that I'm still connected (excellent signal strength). I can still IM.

When I reboot the computer, I can get to the internet for ~ 5 minutes and then I lose it again.

It started this a few months ago. I don't remember making any changes that might be causing the issue.

Any suggestions? Thanks.

 

it does it on wired and wireless, Firefox and IE...