On a bad day I tried to power on my PC. When pushing the power button, it blinked only once and I could see the CPU fan started spinning and suddenly it was stopped. Then everytime I am pushing the power button no response at all. Then I made the power supply off. Then tried again and the same sequence of incident is happenning everytime as I mentioned above.

I was used to try this everyday; and then suddenly on a good day, it was able to boot. I thought may be something was there in the motherboard with loose connection and it is unknowingly/amazingly fixed now. Using for some day, again I observed the same problem as earlier it was.

Now the situation is like I never know if my PC will boot today or not; it is like behaving on its mood.

Please help what may be the root cause or how I can fix this everyday uncertainity.

Thanks in advance.

The most common cause of a problem like that is the capacitors on your motherboard, check to see if any of them are domed or leaking. If any are then they need to be replaced.

What Rik said is pretty correct, though it may be a bad solder joint in the power or battery connector. Unless you are a capable electronics technician, take it or send it in for repair by qualified people.