Go to to your desktop and in the Dock open System Preferences->Network tab. Then in the Network tab at the top in the 'Location' bar use the pull-down to select 'Edit Locations'. In the Locations pop-up click the + button and add a custom named Location (like Home or School, something along that line where you are located). Don't worry because this custom name Location will act the same as Automatic. Just make sure you save this new custom named Location and save it. Lastly rejoin your wireless network.
Another fix is to open /Applications/Utilties/KeyChain Access and delete the entries for you wireless network and when you re-add your password let it save again. This can also help, good luck.