Sorry if anything here is not too descriptive, but I am not very educated on the workings of hard drives.
What happens is that the hard drive can be doing anything, and then it will make a sound. The sound is a bit like a whine, it whines and then the computer will freeze. Programs will still work, and if you were listening to music or using VOIP you could still hear and talk, but everything on the desktop would be unavailable to you. After a bit of time, the computer would unlock and work normally.
I do not know what is wrong with the hard drive, as tests have said everything is fine with it. I have checked and double checked the wires, and both are fine. The power supply seems fine, it is 700 watts and has had no other problems.