A hot computer is a bad computer. Excess heat can cause malfunctions and crashes, and permanently damage your hardware. Although laptops generally put out less heat than desktops (energy efficiency is a higher design priority), they have their own unique problems. They’re rarely as well ventilated as a desktop, and much more difficult to clean.
Avoiding an overheating computer is all about ventilation. If the hot air can’t escape, you’re going to have a problem.
Whenever your laptop is on, make sure that nothing blocks the vents (which are probably on the sides). Don’t put the PC on a pillow or a soft mattress, where it’s likely to sink in and get blocked.
And never, ever put your laptop in a case unless it’s off, hibernated, or in sleep mode.
You’ll rarely find vents at the bottom of a laptop, yet heat tends to accumulate there. If you let dust accumulate in a PC, you’re bound to have problems.