I have the same problem and it can temporarily be resolved without doing a time-consuming red-button reset.
if I go into the Settings and view Satellite signals, then exit, the tuner begins to work again IMMEDIATELY (the small window shows live TV as soon as I go to the View Satellite Signals page) and all channels are back to normal. That remedy has worked. However, the problem will come back at any time (and, yes, I've done the red button reset too).
DirecTV is replacing the HR-24 HD DVR to try to fix.
I answered on a similar thread that I am having the exact same issue.
So I believe DirecTV may be having an issue.
HEre are my specs:
Genie HR34-700 - in the San Fran Bay area. Device is 1 year old.
What is really irritating is this happens when recording a show - so the recording is just black. (but I have audio)
I noticed this become progressively worse over time, so I knew it was something to do with my usage patterns. My DVR had less than 10% free disk space - around 6% when it finally became unusable.
This is what I did to fix it:
I went though the guide - slowly and painfully at first and started DELETING old shows and series that I had watched.
I got it down to about 30% free then I turned off the STB and turned it on again.
Finally, better response! Not great, but at least usable.
Then I went through and deleted everything that I had watched until I had about 90% free - turned off/on again and....
it's back to normal response times!
I also went into my series manager list and removed about 20% of my list of shows that are no longer running, just to free up some CPU cycles, but freeing up disk space was the key for me.
I have seen similar issues on other DVR boxes, but this is the most extreme symptom I have yet to experience. It also explains why everything works so well when you get a "NEW" box!
Bottom line: regularly delete shows you don't want to keep so that your free space doesn't fall below 30%-40% if possible.
This is CLEARLY a poorly tested STB app if a full disk can cause this issue. I hope this helps someone!