I have managed to fix this myself. I removed the hard disc and removed the two partitions, returning it to factory state. I then rebooted the device but this did not solve the issue and the hard disc was still not being recognised, even though it forced me to clear the disc. As a final attempt to resolve the issue, from a powered off state, I inserted a memory stick with the above firmware on it and then bridged the pins TP7 & TP8 on the motherboard and powered up the unit. It beeped on power up but I waited for a second beep before removing the bridge. The device then entered firmware install mode and re-applied the firmware. It then powered up and started working instantly. After a few mins re-setting my configuration (and removing the default admin account), everything is back working again.....phew.