The main cause of problem behind this is the SMPS box that is kept inside the CPU just beside the fan of the CPU. Basically SMPS box is nothing but A switched-mode power supply (switching-mode power supply, SMPS, or simply switcher). It is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power. SMPS transfers power from a source like the electrical power grid to a load (in this case a personal computer) while converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from the input voltage.
Due to defect in the SMPS box, the computer’s CPU takes time to start.
Now to avoid this situation, unless and untill we are an Engineer, simply we have to get the SMPS box replaced.
For information on SMPS box you can refer the official website of wikipedia, a free knowledge encyclopedia.