If you had a wi-fi connection your area that did not block access to others (using the wi-fi router security encryption) then anyone in range of that wi-fi could sign into that wi-fi account.
It is likely the person with that connection has learned how to turn on his encryption so that unauthorized users can not piggyback anymore on this DSL or Cable High speed internet he was broadcasting through wi-fi.
Sometimes people intentionally broadcast their signals free for others to use (expecially in cities) but if you have an account and don't protect it someone can hack into it and take over your computer.
I had my wi-fi encryption off for awhile when I first set up my D-link router but once I learned how to set up the encyption now only notebooks that have my passcode can log into it.
Or the person near you could have just moved and turned off his service.
Note also that Windows SP2 has messed up the existing wi-fi connections of many people -- Windows XP SP2 now has a built in wi-fi utility that works fine but the Intel proset or other utility the notebook used in some cases does not work.
If you updated (either automatically or manually) to Windows SP2 you may have messed up your wi-fi settings and you may in fact still have an open wi-fi account but you just have to reset your wi-fi in windows.
Read the Cnet article on Windows SP2 for this issue.
If you are a student many universities have wi-fi access but likely you have to have a passcode to access it.
I bought a laptop second-hand. The wi-fi worked great for a week. I put the laptop away for two weeks, took it out, and the wi-fi won't connect to the Internet. What are the possible causes?
Do I need to have a wireless account? I didn't have one when I started using the computer.