DW's computer stopped connecting to the WIFI at home. I tried everything I could think of. Finally, I decided the adapter in the computer had died and bought another. I replaced it on the mother board. (Did not want to use a stick because she only has 2 USB ports.) It STILL wouldn't connect. Finally, I discovered that there is a WIFI symbol on a key on the keyboard. I hit it, and the WIFI connected. She had accidentally hit that key and disabled the WIFI.
Oh well, she now has a b/g/n adapter where she only had a b/g adapter before.
ON EDIT:
On re-reading the OP, I see that her computer can see the WIFI signals. That means this is not your problem. I am not going to delete it, however, because someone else may find it useful sometime.
However, some networks require the MAC address to be registered in the system before allowing a computer to connect. At my house, even with the password, you won't be able to connect unless I add your MAC address to my MAC address filter. This should not be a problem on your home WIFI though. It also is not a problem if you try to connect at a McDonalds or Starbucks.