No one has suggested the obvious. Have you cleaned the cache and performed a disc drive defrag? Have you run the latest spyware removers? My wife uses my old laptop and it is so buggy that I set it to run the disc cleanup every time she turns it on. She does a lot of internet surfing and when AVG runs it typically finds 150 pieces of spyware. They frequently lock up her machine also. If the lights are still on I don't think you have any type of hardware problem.

What I would like to find is a list of which processes (shown in the task manager) are not really necessary since they take up so much processing power and can cause you machine to lock up. I must have 50 or 60 processes running on my machine and I am sure that many are useless and could be eliminated. I just don't know which ones they are.