Wifi doesn't work but Skype does (and it's not like the one case you already solved) So. I select a wifi network. Get into safari and int wont load the main page. But I can make calls in skype and with perfect comunication with the caller. (Wifi works for skype) but when I do all the steps you told somebody to do (go to the network preferences. Then "advanced" go to the DNS. And select one of thise numbers (8.8.8.8) (they are not grey for me, they're black) then Ok and then Apply, safari would still not load and skype would kee working. What can I do?
To find the hosts file, open Finder and, in Finder’s menu bar, select Go > Go to Folder. In the box, type the following location and press Return.

/private/etc/hosts


That will show you the Host file.

Double click on it and you will see:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1   localhost
255.255.255.255 broadcasthost
::1             localhost 
fe80::1%lo0 localhost


Yours has to be exactly as this, nothing more or less.

If it is different, let me know so we will fix that.