Could be a dns problem - upstream providers can be flaky* Can he ping or
connect to a site by entering an IP address?

* That's why I always run bind on my linux boxes - works a lot faster too.

He cant ping any site nor enter it via IP.
It just says that std "Connection not found...".
But what gets me is he cant access the modem.
Typing it into the address bar just says "Address not found".

I had a similar problem at one time,the Modem was bad. I had a hard time
convincing my ISP it was bad as they could access it from their side.

It wasn't the modem here. Well, perhaps I shouldn't say that for sure.
I finally was able to get my dad logged into his modem. First problem: a
10.0.0.X address was assigned to the modem. The cable company runs a
172.x.x.x number. So called the isp and they rebooted from their end.

Was able to gain access to the modem now but, not sure why it mattered
to change the ISP side of the IP to gain access to the modem.

He was able to gain access to "some" sites. Not sure what is blocking
them at this point. I have opendns in his modem to get around the ISP
outdated one. www.weather.com is not accessible right now for him.

Im still working on it.