MacBook connects to network over Ethernet but not WiFi
Under System Preferences > Network, choose AirPort, click on Advanced, select the name of your wireless network and click the - button to remove it.  Turn AirPort off, wait a few, turn it back on, and try reconnecting to it.

You might also want to open the Terminal up and run the command:

dscacheutil -flushcache


Failing that, create a brand-new user account on the MacBook, log into that account, and see if it can connect.