|Internal ducts and heat sink fins can be clogged with dust even if the external vents appear to be clear, blow the vents clear with a can of compressed air from computer or office supply store. Open covers on the bottom an repeat.|
Check in Task Manager to see if CPU usage is high when it should be minimum or idle, if it is high, let us know and we can give you some advice on fixing this (possible infection or at least a program or programs running in the background that should not be).
If not these then the laptop will need to be disassembled either for cleaning, or possibly resetting the heat sink or replacing the fan. If you are not up to this type of repair or it is still under warranty, take it to a professional at this point and make sure you tell everything you have already tried since this will save them time and possibly save you money.
You have to be a little bit crazy to keep you from going insane.