DVR Chatter

I just got a 6412 III and connected the rear composite inputs to the output of my DVD player, so i can watch dvd's. when i hit the "input" button on my remote, i get nothing (it stays on digital cable). The box is registering the signal from the remote, but the input source doesn't switch. Are the rear inputs active? I know that the FRONT are not.
(hope this hasnt been answered elsewhere, i looked, but didnt see anything....)

thanks.