One cause of intermittent system problems can be from improper heat sink installation or inadequate cooling of the CPU. Many CPU cooling assemblies now ship with thermal phase change compound applied to the heat sink. A protective label or paper covering is placed over the compound to avoid contamination or damage to the surface of the material. This label must be removed before the initial installation of the heat sink.

A heat sink and fan assembly with phase change compound covered with protective paper.

Remove the protective paper before installing the heat sink on the CPU.

Phase change compound changes from a solid putty-like consistency to a liquid as heat is applied or during normal operation of the processor. In the liquid state, the material can flow and fill small gaps that may exist between the surface of the processor and the heat sink. Once the heat is removed, (such as when the system is powered down,) the phase change compound reverts back to its solid form. If the heat sink is removed, the material may tear, leaving gaps where no compound can conduct heat away from the CPU. For this reason, phase change thermal compound cannot be reused. If the seal between the CPU and the heat sink has been broken, the compound should be completely removed and replaced with thermal transfer compound before reattaching the heat sink.
 

If the seal is broken between the heat sink and CPU, you cannot reuse the compound without risking heat damage. Clean it off and apply fresh compound to the processor before replacing.

Use a credit card to and paper towel to remove all traces of the phase change compound from both the heat sink and the CPU.

Apply a thin layer of heat compound directly to the CPU. Avoid using too much that the extra would be forced out around the processor, and block air flow to the surface.

Only use enough thermal compound to make a thin layer where the heat sink and processor touch. Excess grease will be forced out as the heat sink is locked down to the CPU or socket assembly.