I have a 3 week old 2012 27-inch iMac and this morning I turned it on and it wouldn't connect to the internet. It connected to my home network just fine, just not the internet. I assumed it was my router's fault, but every other device in the house connected to the internet just fine. I have already tried turning it off and on again, many times, as with my router. I have also tried turning the Wi-Fi off and on in System Preferences. Any help?
By "turn it on/ off," do you mean you rebooted the computer? Apple sign in the top left corner > Restart. Sorry if this seems obvious. Just have to start simplest first.
If you have tried rebooting, try the following: