Safari says "can't find server

Power off the router. Unplug it from the wall. Wait a while.

Plug it back to the wall. Power the router on. Wait until all the lights are lit properly. It will take a while.

Restart the computer.

Start up in Safe Mode.

http://support.apple.com/kb/PH11212?viewlocale=en_US

Try the suggestions in this article.

http://support.apple.com/kb/ts1843