It worked when I first plugged the new SD card in (lights, IR, everything). I put it to sleep and set it aside. When I woke it up later to use it, the screen lit up but the touch screen was no longer responsive. Had to turn it off by pulling out the battery connector, after which the screen would no longer light up, the only indication I could get was the power button lighting up.
Battery seems to be okay as I even tried connecting the non-responsive H2O's battery connector to my other H2O to see if it could power it up, and it did.
Just a bit strange as the non-responsive H2O was working with the other H2O's SD card before the new card was put in. Anyway, we had a good five year run and I have a Kobo Forma on the way so I'm not too broken up about it.
Thank you for all your help, davidfor, it is always much appreciated.