Did you reset the router and remove the old computer and setup the new one? Access your router's setup page and check the security settings. Your router might be looking for a mac address that no longer exists--the one for the stolen computer. One way to start to add a computer to the router is to connect them with an ethernet cable temporarily to have the router recognize the new computer while you setup the passwords, workgroup and settings. Check the belkin web site for help with this. Make sure all the names on your network are correct--workgroup, network, passwords, computers, etc. Do not accept the default names. For instance, Win 7 uses WORKGROUP as the workgroup name, while win xp uses MSHOME. Use the Network & Sharing Center on the Win 7 computer to setup the connection. Lots of help there to guide you.

Thanks, I did reset the router and that didn't work. However, I found out the router had a firmware update and loaded it. That seems to have done the trick! Thanks for your response