You first need to go into your Network and Sharing application and click on connect to a new network. It will scan for any available networks you can connect to. Once you have found your network router, click on it and then it will ask you for a network key. Enter that password in there. and then it should let you connect to the network. If it doesn't, then unplug your router and wait at least 10 seconds. (Some routers have a feature that keeps the power on when the plug has been unplugged) If the lights on your router are still on after you have unplugged the router, locate the "Reset" button on the router and quickly press and release the button. Follow the same procedure as described earlier. If it doesn't work, then trash the sucker and buy a new laptop.
sometimes you can have connection overload.... if you have too many devices connecting to it at once, try disabling the connections you are not using (Nook when you are not downloading, Laptop when you aren't using it, etc.) If the signal strength (connection bars) are good and the turning off connections doesn't work I would just cycle/troubleshoot the signal (router and/or laptop) to see if it clears up.