Hardware: Diagnosing Noises from your Hard Drive

A few months back I gave my son my previous computer.  It's not that much slower then the newer machine I built to replace it.  Recently all of a sudden it became unusable as far as performance, it was slow to start, basically bogged down when you try to use it.

When I checked into the problem, I noticed that the hard drive was making a clicking noise.  I hate to say it, generally when hard