|If it's the wireless key you need (it's proper name is a "key" not a password), resetting the router will not reset the wireless key to it's factory default. It stays as it is until you manually change it.|
To discover the wireless key for your router, open your router's configuration utility by typing it's internal IP Number or IP Address into the address-bar of any a web browser, then press <Enter>.
It's internal IP Number depends on what make it is but try one of these:
Note: do not type www. in front of the IP number.