Why does my laptop overheats

You may try first to open your laptop and check if the Cooling Fan & Heatsink cooling grill is completely blocked off with dust build up. The blockage will prevent the heat from getting out off the laptop thus triggering the thermal sensors to auto shutdown your laptop.

If the cleaning of the vents has been completed then it could be something running on the computer that is causing it to run at a high CPU usage. Open up the task manager and sort by the CPU tab and see what processes are running quite high.

If there is a 'NT Kernel and system' running high then there could be some hard drive errors, then a check disk needs to be carried out this can be done by opening up windows explorer and right click on the drive letter - select properties then the tools tab and click on check now button, this will perform a chkdsk and correct any errors that might be occurring. After it has completed then i suggest rebooting of the computer.

Has the processor ever been pulled? If the thermal paste wasn't completely cleaned off and replaced, it won't have good contact with the heat sink. The reason I mention this is that I had a friend with the same problem, who never mentioned that he'd pulled the processor (as an exercise in curiosity) and replaced it. He didn't want to admit it, but once we got everything cleaned up and re-installed properly, it worked fine.