Wi-fi doesn't work...

I have a cable modem connection to a Thai internet network. Works fine. I have an ASUS RT-N10 Router, which I use to connect to an iPad thru Wi-fi in the same apartment. I just bought my GF an ASUS Notebook PC and can't connect to the Wi-fi network(Dink) in our condo. The screen asks for the security code, which I can't find. How can I connect to Dink or get the code?