Acer X223HQ goes on and off continuously in a peculiar manner

My Acer X223HQ flat screen LCD monitor (21.5”) worked well for 2-3 years when connected to a Dell E520 desktop computer.
Suddenly, the monitor (but not the computer) started cycling on and off and I swapped it out for another monitor I had available at the time.
I have now had an opportunity to test it more completely and find that, when the computer is started up from cold, the blue power light on the monitor comes on as expected and stays on for 40 seconds.
During this initial 40 seconds, the computer boots to completion and the boot sequence and the desktop image are clearly shown on the monitor.
Additionally, the mouse and keyboard are fully functional.
So far so good but then the trouble starts.
First the blue power light switches off and stays off for 3 seconds.
Then the orange power light comes on for one second followed by the blue power light again and a fully functioning screen.
This time, however, the blue light (and screen) stays on for only 12 seconds followed by power off for 3 seconds, orange light for one second and blue light and screen on again.
On every successive "cycle", the blue light stays on for shorter and shorter times until stabilizing at about 3 seconds on for the blue light followed by power off for 3 seconds, orange light for one second and so on ad infinitum (or at least for an hour which is as long as I left it).
If I switch everything off and leave it sit for an hour or so, I get the same sequence as described above with the blue power light staying on for 40 seconds on the first cycle and winding down gradually over about 6 or 7 cycles to just three seconds on.
If I switch everything off and leave it for just a minute or two, the monitor still cycles as mentioned above apart from the fact that the blue light and screen stay on for just three seconds even on the first cycle.
Interestingly, the monitor behaves in exactly the same way even if no computer is connected. So, the monitor in this condition does not remain in sleep mode as would be expected.
So, I opened up the monitor and took out both the power supply board and the video board fully expecting to find blown capacitors on one or other of these boards.
However, none were found.
Nevertheless, I replaced 12 (twelve) of the 15 caps on the power board leaving just three untouched (1x10uF/50v, 1x225uF/25v and the large filter cap 120uF/450v).
When I put everything back together, the monitor's behaviour remained just as it was beforehand, in other words, the exactly same on-off cycling sequence was maintained.
I will also mention that the power cable, the VGA cable and the computer all work perfectly with another monitor so they are not at fault.
At this stage I'm confused and would welcome any comments or pointers to what might be happening here and, particularly, how to fix it.
Thanks.