Here's an interesting experience that might help others:
Last night when I swiched my HDFOX-T2 box to standby for the night, it shut down but immediately powered up again. It continued to do this each time I tried to go to standby. As it was getting late, I switched off at the mains and went to bed.
This morning, it was exactly the same, so I disconnected the Seagate 500G portable external drive. The problem was still there so I did a factory reset. Problem solved!
However, on reconnecting the drive, the problem came back. Looking at the recorded programmes, some of the folders and files were missing, so I assumed that the disc had corrupted and did a reformat (using the box). All now seems to be well, but it will be interesting to see how long it lasts!