Hi nicoleb and welcome to GeekPolice!
It is quite usual form wireless routers to be able to detect wireless networks, but unable to connect to them. Various reasons can cause this. The most likely one is that the signal is not strong enough. Another possibility is that the network owner has MAC filtering enabled, thereby blocking unauthorized computers from connecting to the wireless router.
On a sidenote: connecting to a unsecured network might not be legal if it is without consent of the network provider.