I forget where I read it all, but there are a lot of posts about this problem.
EDIT - here is the link:
http://www.aximsite.com/boards/showthread.php?t=69777
It is either in here somewhere or on the Dell Axim forums, but you should be able to find it. I remember at least one case where Dell replaced the motherboard on the laptop with the cooked usb ports. You might want to contact them. Be sure to do it via "chat" rather then over the phone though. My experience with Dell chat has been excellent.