The twin tuner problem turned out to be mislabelled cables among my five feeds off the roof (2 direct A2, 2 through Diseqc plus Aerial). Technomate's advice was to try them out one at a time - this showed that my primary feed to the TM was actually a direct to A2 only connection and my secondary feed was one of the Diseqc feeds. Swapping the A2 direct line for the other Diseqc connection enabled dual recording. My roof-top connections were thus correct all along saving an engineer visit to check them out or change anything.
I still can't watch a third satellite or different TP while the two tuners are recording but believe that is what the 106 patch Technomate is currently working on will provide. Read something similar happened with the 7100 when that came out.
Non-working HDD turned out to be a drive which draws too much current for the TM so overheats and shuts down. It works fine in a powered USB housing and is being replaced as the internal drive.
So, pretty much now fixed... or hope so once patch 106 arrives.
Thanks to everyone for support and encouragement