My Laptop can also be used as a heater!

Any idea on how to diagnose problems with Laptop's thermal padding???I am new to repairing such stuffs.The problem is my laptop's fan gets off after a long time only.Even when i don't run heavy applications or games;this problem occurs.I referred some online help and I understood that thermal padding would have worn out.Or maybe there would be too much dust around the ventilation area of the laptop;which does not allow the heat to escape;heating up the laptop.So far;applications do not get hanged;which is also an indication of poor heat dissipation.

If you have any ideas or some knowledge on online references;please advice.