As i understood you wants to find out the network key..
it would be helpful if u specified the model number of the router.
i hope you having wireless netgear router.
step1:connect the computer to the router.
step2:check the ip address of the computer.to check ip address
-->click on "start" menu
-->go to run
-->type in cmd
-->you could find black window.on black screen type in ipconfig and press enter.
-->it will gives you the ip address from the router.make a note of default gateway address.
step3:open browser window.
step4:on the address bar type the default gateway address and enter.(no www and no http,just type in the gateway address).
step5:enter the router user name and password.
step6:after enter into the router window..you can find the small blue screen in the left side.
step7:click on the option "wireless settings" under SETUP category.
step8:in the wireless settings screen, you can find an option "security options".
Below that you can find your network key.make a note of it.as well as make a note of ssid,channel,mode,authentication type,encrytion strength.
I hope this will help u:-)