If the hard drive were the problem you'd get a blue screen with an error code.
What happens when you change channels or start a recording?
This still sounds like an HDMI handshake issue to me. The fact that switching inputs away and then back fixes the problem helps back that up. When you switch the inputs and then switch back the HD-DVR and TV have to go through a HDMI handshake before it starts showing the channel picture.
My guess is that when your TV and HD-DVR are first turned on something is causing that HDMI handshake to not complete correctly. That is why it doesn't show the picture of the channel you are currently tuned to, but it will bring up the menu, playlist, guide, etc. This also explains why the S-Video output doesn't show any video either. If there is a problem completing the HDMI handshake the DirecTV receivers kill video output to all outputs not just the HDMI, the the composite, S-Video and component outputs will all show the same blank screen.
If you change channels, or start watching a recording with a different resolution it will cause the HDMI handshake to occur again, and that is when your picture comes back. Same thing with changing inputs to a different one and back, it causes a new HDMI handshake to take place.
If I change channels with my HR23 after I have a picture, it takes from 5 to 10 seconds for the channel to switch. Slightly slower than my HR24, but that might be expected. If I use the PREV switch, the channel changes in 3 to 5 seconds. This phenomenon, No Picture After On (NPAO) only happens after the HR23 has been off for a while, like several hours, usually more than two. ON and OFF and ON again every so often always produces a picture. If I turn the HR23 on and get NPAO, and press the RECORD button, nothing happens. If I get NPAO and I quickly PLAY a recorded video from the LIST, I get a picture immediately. Also, to reiterate, if when I have a NPAO and I press PLAY, the time and program status bar oftentimes displays a time and a program that have been over or several hours (more than 1 1/2 hours). I still don't know what to make of that. On the HDMI handshake, I've got some experimenting to do. The HR23 is on HDMI 3. When the HR23 is OFF and I switch to HDMI 3, usually there is a graphic on my screen from the TV that says "NO DATA." Sometimes however, that graphic does not appear. Maybe that means there is no attempt at handshaking at that time? I'll have to check and see if that graphic finally appears after waiting a while before I turn the HR23 on. Also I'll have to see if I get NPAO or an immediate picture depending on whether or not that graphic is on or off. Thanks!