Troubleshooting Brookstone Wireless headphones

Can Anyone help me with this problem with wireless headphones. I bought 2 pairs of these wireless headphones, one for me and the other for my mother. I put mine on my 27 in flatscreen with a HDMI attachment to the cable box. The other I gave my mother but she has only a comcast box connection to the tv. well the headphones don't work. she has a 22in flat screen. I change batteries and put the a/v cables in the right spots, the white and red spots in the tv. well I tried it on my tv, it does work on the 27in but on my 22 in in the spare room, it doesn't. I get a feedback when I put the white/ red in place but no sound. I notice the 22in has a connection from my tv in bedroom to this one. I ran a cable from bedroom tv so it doesn't have a cable box. would that make a difference to get sound. I am totally baffle and will have to return it and get something else. I need suggestions or help. thanks