Just had an HR21 that developed a stuttering problem, and it was due to the hard drive starting to fail. Getting DirecTV to acknowledge the problem and send a replacement was a nightmare. After over an hour of troubleshooting the support analyst claimed the problem wasn't bad enough to warrant replacement, and there was nothing they could do until it entirely failed. It took being transferred to retention and explaining that my next call would be to Dish, who would bring out a brand new Hopper free of charge, to get a replacement. If I were to start over again, I would skip the aggrevation and just say that the receiver won't power on at all. (Hate to encourage telling a fib, but if you've done your due diligence and know that the receiver itself is faulty, it's easier on everyone.)
Since your problem is only intermittent, it may not be as bad as mine was, and you may be able to fix it using the disk utilities:
- Reboot receiver
- When you see "Running receiver self-check" press the SELECT button.
- You will see "Entering Diagnostics Mode"
Once in Diagnostics Mode:
"Hard Drive Utilities"
Start with the short test, as some of the others can take many hours to run. Good luck!