Mac Can't connect to a wireless network

I just moved into a house with some roommates. They have Verizon fios on a wireless actiontec router. My MacBook picks up the signal but connects without asking for the password to join the network. It says that I am connected with the network but I can't actually do anything on safari, it just says not connected to the internet. Looking at Network Configurations it once again will say I'm connected but not give me anything. On my iphone it will ask for the password and will connect but my MacBook doesn't even ask for it. Any clue on how to enter the password so I can really connect? On a side note, I did enter the password a while back before I moved in and successfully connected but now it won't connect. Please help. I hate having to run a wire to my MacBook. Thanks

If you go into System Preferences, Network, Airport, Advanced. You can find the wireless network and change the Key in there which should then let you connect. Were you getting an IP address when you connected and couldnt do anything?

Oh thank you. I am running an older OS so your directions were a tad different but they got me where I needed to go. Thanks for your help. You're a lifesaver.