Wireless from home, but no wifi access

Hi.  I have a Latitude D620 with a Dell Wireless card.  I have absolutely no problem connecting to my wireless internet at home, but any time I bring my computer to a wifi hotspot, it cannot connect.  I "see" the wireless connection through my wifi catcher.  Can highlight it and click connect, but then nothing happens.  Does anyone have any ideas on what is going on?

 

Thanks!