I had a similar problem. One of our laptops just stopped working,
while the other was fine. The other had been in a Dell warehouse being
repaired for the previous week and a half. When it came back it
worked, but there were lots of Windows Updates waiting. After a couple
days, it failed too. I suspect it to be the Windows Update that
triggered the problem, but it was fixed by updating the firmware on the
router.
I don't know what router you're using, but in the notes for the
firmware update for my netgear mr814v2 was something about fixing a
compatability issue with centrino (though my system was not centrino).
Have you tried connecting without encryption? I was able to connect so
long as I wasn't using wep.
Either way, and whatever router you're using, try getting the latest
firmware. Worked for me.
hunwalla