Brian wrote "firmware should be able to use larger cards than the very first one used with it." That suggests that a factory reset would return the camera to a state in which it doesn't know what memory card it had and that, having done a factory reset, I could install a larger capacity SDHC, copy all folders and files (which I have already proved can be done successfully with the 4Gb SDHC) and that would resolve the issue.
I wrote in my first post "The camera and the computer have long since refused to talk to each other so, in order to transfer files, I have to first transfer the card to a card reader - a bit of pain." This has now worsened. I went to change the date and and time to find this option does not appear in the menu <Menu><Setup> which now includes ONLY <Copy> and <Firmware Version> but does NOT include <Factory Reset> - unless I'm looking in the wrong place?
All the useful suggestions about using a mobile telephone and tablets is, unfortunately not useful to me as I don't have such things (and at my age don't really want to go there). Similarly I don't really want to replace the camera which I'm used to - unless absolutely essential.
Where do I go from here?