What kind of Router is it... make model? The security key is something that you setup... most routers have a logon id setup by the manufacturer its normaly user=admin and the Password is blank.. If you forgot the security key just unplug it and then set it up again.
Unplugging will not reset the the password. You would need to press the reset button on back of router. However you will need to access your routers configuration by physically connecting your laptop to the router with a network cable.
In IE you type the routers address (192.168.1.?) this will get you to the config. scrn.
Go to security tab and unhide password. while there make note of protocol. WEP,WPA,WPA2,etc..
If you tell us what kind of router you have we can give you the address (?)