HDMI not working on box (only DVR box works)

I have purchased updated TV's.  I can only get the HDMI hookups to work on the DVR box.  My other additional boxes don't work with direct plug in.  I have to use an RCA (red, yellow, white) to HDMI converter for the boxes to work with the TV HDMI hook up.  WHY ??????  Am I doing something wrong.  Even the Best Buy Geek Squad couldn't figure out why they weren't working.