How to fix external hardrive?

It could be anything from failed hardware to a broken cable. Try switching cables and computer ports. If that doesn't work, try booting your computer with the hard drive attached.

As for the clicking, that's normal. That just means that your hard drive is working.

Clicking is usually a bad sign, if it's not a normal clicking sound that you've heard the drive make before. You could have a failing drive on your hands. Western Digital does have a diagnostics tool that you can run for drive performance and SMART results. I'm not sure of the exact name, but you can find it on their website. It'll give you a better idea if something is failing or could be wrong before you start tearing it apart or consider getting something different.

If the utility does give you disturbing information, I'd start copying data off to prevent data loss, as obviously that's the most important thing at that point.

You probably wan't to bring it to your local Best Buy for the Geek Squad to look at it although I don't like their people there they do have the equipment to fix the things you need them too.