Contact between processor and heatsink in PC

Today i just removed my fan of the processor in my PC. Then i observed a paste like substance which is in between the contact of heatsink and processor . Then i replaced the fan. But now i doubt that the 'paste' in between for efficient contact and heat transfer may be affected .
What should i do now? Should i apply new paste by rubbing the old one ? If yes then what is the name of that substance?
Now pc is working fine but i doubt the efficiency of the contact between the processor and fan heatsink.

no its only to stick up with processor ,,,, leave it as its is ,,,,

Sure? But still i doubt.....

I had seen such paste in between power amplifier ic and heatsink which is screwed tightly... Then why its used in that case? I think its for correct contact betwee the small heat sink in ic and external large heat sink. I think that heat conducting paste may fill the pits in irregular metal surface and increase the surface contact efficiency. Am i right???

If i am right, then i think , since i removed the fan and replaced it again then that contact efficiency may be reduced since i disturbed the paste while removing the fan.
I heard desktop processors like intel will produce large heat while working.

That is to dissipate heat....Its a thermal paste..as long as you didn mess up with the thermal you should be fine....If you have removed the thermal paste..you need to do a repasting done ASAP..else you may fry your processor..

Vinodstanur, you are correct. The paste is a 'filler' to increase the contact area between the heat source (processor) and the heat sink so thermal conductivity is as great as possible. The paste is usually silicone grease with added zinc oxide or some other metallic compound. If you can guarantee to replace the heat sink exactly where it was, so the paste lies in its original position then do so, otherwise try to even it out on both surfaces before reassembling them. It sometimes helps to slightly twist the surfaces together so trapped air bubbles are squeezed out. The objective is to maximize contact and minimize voids which could cause uneven heat distribution. If necessary, you can remove and replace the paste with new "heat sink compound" which you can buy at most electronics stores.

Brian.

It is exactly like Brian states, the paste is to improve the thermal conductivity between the CPU and the fan block. these may appear to smooth but under a microscope they are not. The paste increases the contact area by filling in a gooves etc on the 2 surfaces. This is a very basic article that explains it Thermal Paste and How To Use It

Usually the heatsink that comes with the cpu uses a thermal pad which does the same job as the thermal grease but it has worse thermal transfer characteristics, the advantage of thermal pad is that it doesn't spill since it is much stiffer than the thermal paste.
It is very easy to distinguish them, a thermal pad is a square looking like this

If you want to apply new thermal paste you have to clean the old one, I use isopropyl alcohol to clean both surfaces.
There are plenty of guides how to apply thermal paste if you do a search.

Alex