1. Forgotten WEP or WPA Security Key or Passphrase
Are you trying to connect another Wi-Fi computer or device, but don't remember the security key or passphrase set on your router? Don't worry: It's easy to find your WEP key or WPA/WPA2 passphrase.
If you have a computer with Windows Vista or 7 that is currently configured with the Wi-Fi router, you can simply open up the network properties to see the security key/passphrase. You can't do this in Windows XP, however, since the security key/passphrase can't be unmasked like in later versions of Windows.
To find your key/passphrase in Windows Vista or 7, start by bringing up the list of available wireless networks. In Vista, click Start > Connect To, or in Windows 7, simply click the Network icon in the lower right corner. Then right-click your network name, select Properties, and click the Security tab. Check the Show Characters box and you'll see the key/passphrase. Also take note of the Security and Encryption types.
If you can't use a Windows Vista or 7 PC to lookup your security key/passphrase, you can use a tool called WirelessKeyView. It recovers the keys/passphrases stored by Windows. Download and run it on any PC that is or has been configured with the Wi-Fi network.
2. Forgotten Router Password
To change a router's settings, you login to the Web-based interface by typing the router's IP address into a browser and logging in with a username and password. During the setup wizard of some routers, you're prompted to change the default password. If you aren't sure that you've created a new one, first try the default.
Most Linksys and D-Link routers use "admin" for both the default username and password, or just for the username and a blank password. You can look up the defaults for your particular model here. If your Internet Service Provider installed your router, contact them for the login info.
If you've logged into the router before, you might see if the Network Password Recovery tool can retrieve the login credentials on the PC you logged in from before.
If it looks like you set a password but can't remember or recover it, you can quickly reset the router back to factory defaults. However, this will reset everything so you'll have to reconfigure your wireless security and maybe your Internet connection settings. To reset hold in the small reset button on the back of the router for up to 30 seconds. Then you can connect and login with the default credentials.