Sudden wi-fi connection issues - I am baffled

I have been suddenly having Wi-Fi problems - this week
I have a SMC 2532WB card that until last week worked fine. Windows XP Home on a laptop. Here is the scenario. I have been unable to get online on two unlocked Linksys routers that I have accessed before and I know that they are unlocked because someone I was with could get online.

Local coffee shop and library - I have acessed both of these before.

I know the card is OK because I can ping the router and get a reply
but no internet or email. The card utility shows great signal and link quality.

So I seem to be associated but not authenticated. I have not
changed the computer configuration that I am aware of.

I have tried it with the zone alarm zone firewall off I do not use windows
wireless settings ( though I did try that also and it did not make a differance
my card comes with a nice utility that has always worked.

My wireless Linksys router works at home fine but on that router I use Mac addresses filters.

All my network/TCP/IP settings look normal

I would appreciate any ideas or suggestions - I am baffled.



Thanks for any ideas.