When ever I am brought a system with the same issues, I always use the Microsoft Sysinternals Suite Process Explorer. I find that it allows me to pinpoint issues quickly. I was using these tools before they were bought by Microsoft. They are a great set of tools. Just a suggestion.
As for the information regarding the dirt and dust the inhabits all laptops, you are correct, they must be clean on a regular basis to keep from overheating, odd things from happening.