If you lost or forgot administrator password then it is impossible to view the serial key on the Wi-Fi wireless gateway or router, or need to setup new computer to access the Internet through same wireless network adapter or Wi-Fi hotspot.
Here are some methods –
Using Windows 7
If you are using window 7 then the quickest way to get the network security key for an existing wireless connection, is from the PC or computer which is currently connected to the wireless network.
Go to Control Panel -> Network and Internet -> Network and Sharing Center.
Click on Manage wireless networks on the left pane.
A list of wireless networks that the PC used to connect to with saved password or security key. Click to highlight on a wireless network connection that user wants to view its network security key, and the right click on it and select Properties.
Click on Security tab.
The network security key for the wireless network is hidden by asterisk by default. Instead of using utilities to reveal, display or show original characters of password or key hidden behind asterisks, click on Show characters button to reveal and display the actual original network security key on screen.
Using Default username and password –
Type the ip in browser.
Enter the default username and password. Mostly username is admin and password is admin or 1234 or password and login.
Go to the Wireless tab find something called password. Write down your password and put it in a safe place in case you forget it again.
Or find encryption type and select the Encryption mode to none.
Then Save the setting.
Reset the Router
You can reset the router by pressing reset button which is on the backside of router. To reset this press the button by using pin or pen.
Use Wirelesskey View
WirelessKeyView recovers all wireless network security keys/passwords (WEP/WPA) stored in your computer by the 'Wireless Zero Configuration' service of Windows XP or by the 'WLAN AutoConfig' service of Windows Vista, Windows 7, Windows 8, and Windows Server 2008. It allows you to easily save all keys to text/html/xml file, or copy a single key to the clipboard. You can also export your wireless keys into a file and import these keys into another compute.