How can I hook up vcr, dvd, set-top box to tv?

I have a RCA television, approximately 9 years old and would like to connect it to my AWA video player, my Bush set-top box and my Telefunken dvd player. Can anyone help me with the connection of the video player. Currently we can get as far as having a video tape playing the sound but with no picture. It was working before the set-top box was added but I want to have them all working. There seems to be enough connection 'ports' for all to be there, but we're just not close enough. Thank-you