Many thanks for your comments. I tried some things after your reply, ahd there have been some further developments.
First, some specific answers to your suggestions. The keyboard did not come off its ribbon, and I don't know how to determine whether the motherboard is intact. I disassembled down to removing the fan, but don't know what to look for on the motherboard. And with the keyboard off, I don't know how to switch it on to locate the 'click.'
But there has been some kind of change. After receiving your reply, I turned it on, and surprisingly it stayed on, though moving very slowly, and I got into the BIOS where nothing seemed amiss. The fan was working fine, so apparently that isn't the problem, and the motherboard isn't completely dead. It did look for the hard drive which I had removed to salvage the data. It then rebooted to a Partition Magic floppy, but here was nothing to do without a hard drive. Then it rebooted to the IBM splash, but after a long wait it went black and back to the click routine.
Since then I reinstalled the hard drive, but now get only clicks with or without it. Is there anything in this that rings a bell for you?