go to start>run
type "command" and click OK or press enter
type "ipconfig", press enter
open an internet browser window (internet exporer/netscape/firefox...), and type in what you see in the command prompt window for "default gateway"
a password box will pop up, if you don't remember that password, try u/n: default and p/w: admin, or u/n: [blank] p/w: admin
go to the "wireless" section and look for "encryption" or "security" or something along those lines (it is different for different brands)
the key will be there somewhere