Both old and new hard drive completely pass full mfg diags. Starting to wonder if it is the power supply - if I let it sit unplugged long enough, either drive will boot and work for a while, then either go into a reboot cycle or sit at the almost done screen. At this point I'm starting to wonder if I just give up and replace it with a Roamio Plus. I could either return the 2TB drive I just purchased, use it to upgrade a factory 746 unit I have, or use it in the Roamio. I could also throw more money at the XL with a power supply, assuming it's a safe bet that is the problem. I'm certainly not looking for an excuse to spend $399 on a Roamio. With 3 Premieres (2 x 746, 1 x 748, 1 x 758), 1 Tivo HD, 2 Minis, and a Stream, I feel like I have the market cornered. I guess looking for anything obvious I might have missed.