It’s hard to see how clearing the CMOS has cured this problem, I am glad for you that it has but I am not so sure that this was the cause I have never seen this issue cured by clearing the CMOS and I have repaired thousands of computers in my time..
If this problem recurs then I would try a new power supply.
Here it is 2 months later and the same problem at startup occured. This time I unplugged the power cord from the power supply and turned the switch on and off a couple of times to drain the PSU power totally and it seemed to solve the problem. Maybe a bad capacitor in the PSU? I do not know exactly but am now convinced it is the PSU THANKS