Thanks for the welcome, MacsBug. Sadly I'm not connected to any internet backup service, hence the only thing in my Sys Pref under Internet a/cs is hotmail, which never did link to my apple mail anyhow. I'm going to go into town on Friday to the Genius Bar and hope they can help.
I know it has to do with my running OSX 10.11.6, but that was deliberate as I have apps that won't run under later operating systems. My iMac died 2 yrs ago and I've been meaning to buy another Mac but just haven't got around to it - and the cost is somewhat prohibative. This has now forced my hand.
Back to the calendar. I did a backup yesterday and tried something that didn't work. I thought by setting my global date back a month to last Dec, the system wouldn't try to update the holidays, and I could at least see my forthcoming appts. Theoretically, it should have worked, but the jolly thing still tried to update. Then, a minute later, it went blank.
Thanks for your reply; it is appreciated.