Wireless connection problem

Hello,

i down grade my dell 1525 from Vista to windows XP sp2 my problem now is that connection of my wireless router to my laptor it's not able to browse any web site and there a message on wireless connection icon no valid untitication, signal ok and also if i use the dell wlan utility i can see the available wireless connection but on the windows xp icon wireless connection if you view available wireless connection ther no available wireless connection but on dell wlan utility there is, it show all available wireless connections. so i try to remove dell utility, then try again windows xp wireless connection and view available connection it show, i can connect but not able to browse any internet site and also showing on wireless icon connection no valid untitication