software update killed my internet connection

Hello,
I just installed a software update today 7/3/10. It was, iTunes, Security and something else.
I then tried to go back to buying a coffee machine online but my internet connection was gone. I can't get it back. Airport is working but there are no networks showing and I can't get the iMac to see the existing networks. All the laptops are working fine, I did not install the update on them.
Can anyone help?

iMac 3.06 GHz, Intel Core 2 Duo, 4GB, OS X 10.6.2

Thanks, Barbara

Go to system preferences>network>assist me tab.
If that doesn't fix it, install this
and then try the assist me again tab again.