Where do i find my security key

[xCoorsx]

i have a pc connected to the internet but i am trying to connect another pc to it also and its prompting me to put security key in the one not connected. where is it and how do i find it using the pc that is connected?

 

[Emerald]

http://www.tomshardware.com/forum/38111-43-find-change-wireless-security