PC hard drive makes clicking sound?

There is also the possibility that nothing is wrong with your hard drive at all. If you have a small amount of RAM in your computer, or if some of your RAM has gotten corrupted recently then the clicking could just be the page files accessing your hard drive for more memory signaling that you just need more RAM. Accessing the hard drive for extra memory is natural and harmless but it does take longer and is less efficient than the actual RAM itself, but just to be sure, I'd back everything up anyways.