I just wanted to pass this on. I have spent more than six weeks tring to figure out why I was having intermitten problems with HDs. They would click; seek times were erratic; occasionally the computer would refuse to go to the BIOS setup; on one HD the access time dropped in half; and one time a drive just disappeared. Yhen things would be fine for a while.
After trying different SATA cables and going through every possible permutation of hardware setup, I found the answer today. One of my power connectors was easy to insert. This is noticable as they are usually impossible to seat and remove. I noticed when I touched it with the computer on, the drive clicked. I was able to repeat this with another drive.
Clearly this cable was not delivering reliable power to the drive, and my problem kept moving as I would try different hardware connections and plug in something else to this connector.
In the future, any Molex connector I see that is easy to insert goes in the trash.