From my experience: Freezes are almost always related to a bad PSU or faulty voltage regulators on the board. Overheating may be an issue, but on modern processors there are security options enabled. At first they will reduce clockspeed and voltage when overheating, if that isn't enough they shut down the system. Normally they don't freeze. Cleaning the cooling system is always a good idea, of course, try it and have a look at the temperatures when compiling the kernel.
If overheating isn't the problem try it with a different PSU and look for bend capacitors on the board.
Last edited by TobiSGD; 01-05-2012 at 12:04 PM.