Xbox 360 Help getting Roku TV to get signal

[Horrorstory]

Hey all. I just got a refurbished Xbox 360 to play Skyrim on. Since this Xbox doesn't have hdmi im using the av cables that came with it that the previous owner used. I have everything connected properly but everytime I go into the av app on our tv it says, No signal (is it on?). I've been looking for help everywhere, even the guy I bought it off is trying to help, but I just can't get it to find the signal. All help appreciated. Thank you.