I finally figured out what was wrong with the hard disk recorder from my bedroom. There's a power switch on the back as well as the button on the front, which was partially concealed by the carpet tape I used to stop the SCART plug coming out. I must have accidentally switched it off while I was disconnecting it to bring it downstairs. And of course the loose end of the tape (once the plug was removed) ended up covering it completely....

This means I only need one Freeview receiver, which is good, and makes me reasonably confident that there isn't a curse upon my appliances. It's just a shame that it also shows me to be horribly unobservant!