System preferences > network > WiFi...
click ( Assist me ) > diagnostics.
follow the procedure and do what it says.
... System preferences > Network > WiFi ...
click ( Assist me ) > Setup Assistant ...
... set it up again from scratch, being sure to establish a new "Location", NOT Automatic.Mac Pro (Early 2009), Mac OS X (10.6.8), & Server, PPC, & AppleTalk Printers
What wifi router do you use?
Are the other laptops running Mac or Windows and how old are they and the router?
Your 2012 MacBook Pro and your router may not be talking to each other (hopefully the Setup Assistant will work) or it needs firmware update.
I had a phone that was interferring with network and had to take the phone out and have the phone (cable phone) rebooted.
Forums for MacBooks and Lion: