WESTERN DIGITAL EXTERNAL HARD DRIVE. I have a western digital external hard drive "my

Question

I have a western digital external hard drive "my book" 320 GB model # WD3200D032 that doesn't show up as being a connected drive on my computer but when it is plugged in my computer says that it has detected it and that it is ready for use...also it makes a clicking noise when it is first connected. I have used it before and put data onto it so it has been working before I am just wondering what made it stop working...any ideas? Thank you