Internet connection after logging in

For some reason my MacBook Pro is not connecting directly to my network when I log into my Mac. Every time I have to manually connect to my router because for some reason it is not automatically doing that. What should I do to automatically connect to my router?

I have tried to look into the system preferences << Network. But I don't seem to see an option that will allow me to connect to my router automatically.

Thanks for any help.

(I have a mountain lion operating system)

Jona