Thanks for your replies.
I was aware that MD mode had to be used for a disc to play on the deck, but as WMP did not recognise it, I switched to HiMd for recording, hoping the JE480 would recognise it was an MD disc and adjust accordingly. Obviously this was not the case. I have formatted the disc and now have a 'blank disc.' I have the latest 64bit net driver for Windows 7 on my computer. I have Sonic Stage 4.3 Ultimate edition on my computer and discs recorded on the computer (in NetMD mode) play fine on the deck. ( I wish there was a HiMd deck available in Europe, though the Onkyo price would be hugely prohibiting.) I wanted to use the WMP because Sonic Stage is fickle and volatile, but the Ultimate edition seems to be a great improvement on previous editions. I will probably stay with that, and will not install a virtual disk for the sake of a single function which, as you say, will only lead to tears. My humble ambition was to enjoy the basic functions of the deck and the player and, for the moment at least, I can do that.
Thanks again.