Wireless does not get an Ip address until I plug in the wired RJ45 plug.

I have a dell dimension 5150 tower.
Windows XP with SP2.
Linksys Wireless card.
Linksys wireless router.
Wireless does not get an Ip address until I plug in the wired RJ45 plug.
I have installed different wireless cards.
I have tryed 2 other routers from D-Link.
I have reinstalled windows XP SP2 from the dell recovery cd.
I have uninstalled & reinstalled the latest drivers from the internet.
I have setup a ststic IP address with static DNS address’s.
The card connects to the wireless router and authentictes but does not get an IP address untill I plug in a rj45 plug into the onboard network connection.
I hope someone has seen this before and can help. Thanks.