Thank you very much. Actually, late last night I solved the problem, by going to Control Panel>Administrative Tools>Computer Management>Device Manager. There was "Archos"! I right-clicked, selected "Update Program", and it told me it was applying "MTP".
It appears that just installing Windows Media Player isn't enough: one has manually to apply its Media Transfer Protocol to the new device. Wierd.
Anyway, thanks again. I suggest leaving this thread up because I found numerous references to this problem around the 'net, but not the "right", or my, answer. I have no doubt your way would work, also the suggestion from Microsoft Answers of using MS Fix-it. I'ld like to save someone else the stress of wondering whether they have bought a "white elephant"!