Connecting to wireless network

I have an old dell desktop that has Windoes XP software.  I cannot connect to my wireless network.  I aleays get a limited connectivity alert but my signal strenght is good.  I have a bad IP address starting with a 169.  It won't let me get a new IP address.  Has anybody have any suggestions on getting connected.  Do I need to reset any firewall settings or anything?  Just recently I did a download on a Windoes update for a service pack 3.  Would that had mewss up my IP settings?  HELP?