Ubuntu :: Still Have Wireless Connection But Lost Internet

Three months ago my daughter went off to college with a new computer. I zapped her old system and successfully installed Ubuntu 9.04 from a CD. Everything worked fine including all the peripherals and the wireless internet connection. I was able to download and update applications without a hitch. Great system and so much cleaner and quicker than Win XP on the old machine. Then the system was shut down and lay idle for three months.When I fired it up a couple of days ago, all seemed normal except I could no longer access the internet even though the wireless network icon showed four or five bars. I first discovered the problem when I tried to update though Update Manager and noticed that 22 identified files could not be fetched. Neither Firefox, Skype nor Goodgle Earth can connect.

The router is a Linksys WRT54G router that connects to the computer through a Linksys WUSB54G USB network adapter. The router serves three other non-Linux computers without a problem, including one using the same model network adapter.I don't have much experience with Ubuntu, but this is some of the information I have been able to generate.

I tried a few of the recommendations found in other sites, but nothing seems to do the job. I am perplexed because everything was great until I shut down the system for three months and then started it up again. I appreciate any assistance and would be happy to provide additional information as requested.