How do I find the WEP key for my belkin router? PLEASE ANSWER?

I can't find the WEP key anywhere! it isn't on the side or bottom or anywhere on the router, and it isn't in any of the security settings or regular settings. One time i tried to make a WEP key, but it restricted my internet until i put it back on what it was before i changed it to WEP key (which is WPA/WPA2-Personal(PSK) ) PLEASE HELP. I am trying to connect to my Nintendo DS Wi Fi!!!!!!!!