No on demand interface

For roughly the past week I haven't been able to do anything in the On Demand channel. When I go to OD there are ads but no interface. Pressing the guide button again brings up the regular menu. So basically my OD is a regular channel running ads, not a means to access options. Would this be related to the upcoming digital switch?  My box is old enough I'm assuming it will need to be replaced to keep up with the changes. I forget the model, but the menu doesn't show the current channel in a window like my slightly newer box, if that's any indication of its age.