In the last hour I've:
a) updated the BIOS
b) replaced the old 2 x 1Gb DDR RAM with 2 x 2Gb DDR RAM
c) done 12 Vista updates
Probably, in hindsight, shouldn't have done all three things at the same time (well, stages 1 & 2 of Windows update were done before PC was rebooted but *after* BIOS update .. ). So there was a lot of "New Hardware Found" to sit through after it finally did return me back to a Windows desktop.
Now I've got to power it down again and swap over the power splitter with a new one and see if that allows the SATA drive to work. If not, then I'll have to put in another one (I've got spares) and then see if I can rescue the data via a USB caddy.