Connected to network, browser, mail fail

My mother-in-law visited us today to take computer lessons from my son.
Her Win 7 - 32 bit Sony Vaio connected simply to our home Wifi network, but we were unable to produce a web page in Firefox, IE8 or Chrome. Her mail client Thunderbird was not able to connect to the server. What did work, was Skype.

We deactivated the firewall, to no avail. We looked at the AVG-settings, etc.

When my mother-in-law returned to her home and connected to her own network, everything worked again.

Does anyone have a clou? Next computer lesson in 1 week!

In other words the LAN worked for printer and file sharing but there was no internet connectivity for her computer. Correct?

We did not test printer and file sharing. Skype worked to our surprise, browser and mail client could not connect to the internet.

chezzo said:

We did not test printer and file sharing. Skype worked to our surprise, browser and mail client could not connect to the internet.

If skype worked so that you could actually make a phone call, the internet connectivity must be in good shape. Did you try other computers at the same time just to make sure it wasn't a router or temporary ISP problem? As far as mail programs go, her client was/is set up to work with her ISP which may be different that yours, so sending mail may require a special setup although receiving should still work.