|"I opened my laptop and saw that Thermal pad(paste) between Intel processor and heat sink is melted completly"|
How would you know that without removing the heatsink? As I stated above, the pad is supposed to melt...that's what it's designed to do. Pads are generally made from paraffin wax. When the CPU get's hot, the wax melts & spreads out, filling in all the microscopic irregularities in the two surfaces.
If you removed the heatsink, you have no choice but to thoroughly clean the mating surfaces of all traces of the pad, then apply a tiny dab of paste approx the size of a grain of rice. It should NOT be spread around...just let it sit on the CPU core. When you lockdown the heatsink, the paste will spread out to fill in the gaps.