Q: Can't find server.

Power off the router. Wait awhile. Power it back on. Wait until all the lights are lit up properly.

It will take a while.   Restart the computer.

Start up in Safe Mode

http://support.apple.com/kb/PH11212

For more info:

https://support.apple.com/us-us/ts1843

1. Safari > Preferences > Extensions

    Turn off Extensions if any and launch Safari again to test.

    Turn on those one by one and test.

2. Delete Safari .plist file.

   Quit all applications. Click on an empty spot on the desktop to activate Finder.

   Hold the “Option” key down and click the "Go" menu in the Finder menu bar.

   Select “Library” from the drop down.

   Library > Preferences >  com.apple.Safari.plist

   Right click it and select  "Move  to Trash".  Close Finder window.

   Please don’t empty the Trash.

   Restart. Launch Safari.

  Test Safari.

   If this doesn’t help;

   Put back the com.apple.Safari.plist

   Right click the Trash icon in the Dock and select “Open”

   Right click on the com.apple.Safari.plist and select “Put Back”.

Non-responsive DNS server or invalid DNS configuration can cause long delay before webpages load - Apple Support