The only way to know what part it is, is to swap parts.
I do suspect incorrect assembly such as an extra motherboard mounting post or maybe a nearly overloaded PSU but there are NO PART DETAILS HERE. You may be stuck with a repair shop.
During a heavy rainy day, I tried to switch ON the PC by pressing the power button on the CASE, There was NO RESPONSE, I tried pressing it a few times, still NO RESPONSE, I removed the case and removed all the components cleaned the DUST inside the case and again assembled everything back together, and tried switching on the PC, by pressing the power button on the case, still NO RESPONSE.
I tried to JUMPSTART, still NO RESPONSE.
I took it to the service centre, in service centre it turned ON,
When I brought it back home again the same issue appeared.
And suddenly when I tried to turn ON the PC on the late-night it started!!
The PC worked fine for the next 2-3 weeks, it started whenever I wanted, had no issues with the PC.
Again there was a heavy rainy day, during when I tried to switch on the PC by pressing the Power button on the PC CASE. I got NO RESPONSE.
Since this problem first appeared on a rainy day, it appeared again on a rainy day I assumed, the problem has something to do with the TEMPERATURE OR MOISTURE or SOMETHING RELATED TO DAMPNESS.
I did not use the PC for the next few consecutive rainy days, Then there was a nice sunny day, I tried to switch on the PC by pressing the POWER BUTTON on the pc case, NO RESPONSE!. I removed the two side covers of the PC case, I took it outside and kept in the sunshine, to let the sunshine fall all over the PC, so that it may get heated.
After an hour, I brought the PC into the home and tried starting by switching on, by pressing the POWER BUTTON on the PC CASE,
TO MY SURPRISE, IT STARTED.
So till today every time if I want to start my PC after turning it OFF after a long 6+ hours off the gap, I just can't turn on by pressing the POWER BUTTON on the PC CASE, I have to take the PC outside to let the sunshine to fall all over the PC so that it gets heated up for an hour, then I can bring in the PC and switch it ON.
Some people I know suggested it might be a cold soldering issue, which is a case when the soldering on the motherboard might break off, but when it is heated, the alloy would expand and would make contact, leading it to turn ON.
I also tested the PSU with paper clip testing, the fans were spinning, which indicated the PSU is fine.
I just can't claim warranty without knowing exactly which component is at fault,
is it PSU OR MOTHERBOARD OR SOME OTHER parts??