Open Airport Utility located in HD > Applications > Utilities
Select your connection on the left then click Manual Setup then select AirPort from the menu then select the Wireless tab.
Type in your password. Type again to verify then click Update.
If that won't work, open Keychain Access located in the same Utilities folder.
Select Password on the left.
Type base station in the search field top right corner of that window.
Then right or control click that keychain then click Delete.
Now go back to the Wirless tab in Airport Utility. Re enter your password then click Update again.