The Problem: All of a sudden, your SSID or Wi-Fi network name is no longer listed when you click to see available wireless networks. There are various reasons this might happen, and it's not an uncommon occurrence.
If you see your wireless network listed, right-click on its icon and click Properties. Check the option "Connect even if the network is not broadcasting its name (SSID)."
If you don't see your wireless network listed, click "Add" then select "Manually connect to a wireless network" and put your wireless information in.
Mac users: You can also "force-join" an SSID that has stopped broadcasting through a Mac's Airport Utility. Select to join "Other" and type in the name of the network and password.
Of course, you still want to find out why your SSID stopped broadcasting. Check to make sure broadcasting was not inadvertently disabled in the router's software, reboot the router, and check for any software updates.
Internet Connection Tips; The Wireless Network's Name/SSID Disappeared