Why does my laptop get so hot its a lenovo n500?

It works really good its just that lately the bottom gets really hot. The fan is clean i checked it i took the laptop appart and cleaned it and it continuets to get hot the fans never blocked it just gets hot for no reason and then eventually over heats and shuts off. My friend has the exact same laptop and it doesn't do that and hers is disty and the fans usually blocked off… What's wrong with mine. At the moment its on my lap and its really hot and i don't know why

Get a cooling fan to rest it on. I have a Belkin with a USB plug. It cools my laptops. Both my work and home PCs run hot.

I can't tho, i use it on my couch and bed and its never on a table the fans would be blocked due to the fact its on the bottom not the side

I'm thinking the hdd is causing the problem it seems like it's in the area where the hdd is, could be wrong, if not under warranty i would have it chewck by a pc repair shop