I am having the problem of "connection timed out" suddenly after almost two years of use of the same internet connection.

I had left my apple to download an update on OS Lion overnight and found that the Mac had been disconnected from the internet with a window showing the words 'Connection timed out". I have tried all sort of stuff including turning off and switching on my modem, the Mac, deleting entirely the key chain access (at the loss of all my other passwords which I am now rebuilding), deleting the network in my Settings and trying Assist Me to register again, all in VAIN!

Please help.