Originally Posted by NashvilleKat
I'll guess.....power cord.
If not that, then maybe the power cord.
Or, it could be the power cord.
If you mean the cord from the wall socket that brings the 120AC into the TiVo power supply, if it were bad the OP wouldn't be getting the original Welcome screen.
I thought about maybe the SATA data cable had gone bad, but the OP sayeth they swapped in a power supply from on of the working units, and on this model that means a different combo data/power cable.
However, it did trigger a thought.
HEY, ORIGINAL POSTER!
Do you, or did you, have an external drive attached to any of those S3s?