Common problem, i experience it all the time but it can be solved. Are you using the older version of mac if yes go software update and install the new updated version. Are you able to connect to the internet with a ethernet cable. First go to network utility. Go to spotlight and search for it. Type network utility. In my next post i will show you the picture. Post me what you see. Next go to system preference and click on network. The next few steps you must be an administrator to do it. Click on assist me and click on diagnositcs. The network diagonistics will appear. All the button on the left should be green in colour, post what you see. Follow the onscreen instruction in the network diagonsitcs. See my next post