My Tivo HD wouldn't boot up any more. When I power cycle it, it goes to the Welcome! Powering Up screen briefly, then the screen goes dark, and nothing comes on. The green light on the front panel flashes twice every second. I let it go overnight, and this morning, still green light flashing and no video. I was using HDMI. I switched to component, and power cycled again, on Component, I don't even see the Power Up screen. Back to HDMI and I still see the Power Up screen. the yellow light does not flash when I hit a remote control key either. Any idea what's broken? HDD? Power source?