This post is for information only, since I seem to have found a solution.
Every time I've powered on my TV since September 19, 2013, my TV screen has been blank (black with green INPUT 1 in top corner). As a temporary solution, I discovered I could press the up/down channel button once, which would always bring up the following error message:
AN ERROR OCCURRED. No application focused, returning focus to last active application.
When I clicked the OK button, the live TV picture would return again - at least until the next time I turned off my TV. I noticed that I also lost all my channels above Ch 289 (i.e., PPV and Galaxy Music channels) in the guide about the same time that these error messages started.
I followed [shaw]ali's suggestion here in the TV forum and rebooted my PVR by holding down the Master Power key on my remote for about 20 to 30 seconds and this seems to have solved the problem.