A spin-up followed by several clicks in a hard drive means it is trying to read data and had an error. It sends this message to the operating system that requested the data, and the OS tells it to try again. This sequence will proceed several times (usually 5) before the OS gives up and tells you it cannot retrieve the data you wanted.
Now, at the very beginning, you did not ask for data. It was just the OS trying to establish a connection to the HDD. So after 5 tries it gives up and does not TELL you it had a problem. It simply does not acknowledge the existence of the drive it can't talk to.
The problem could be the hardware side of the HDD, or it could be corrupted data (including data in the disk directory or FAT system). As corkyg says, download and try the WD testing utilities. If you're lucky it can find a fixable problem, and the whole disk will be OK again. Or, at least, a work-around that would allow you to recover most of the drive's data and lose only a little bit.
Faint hope clause: I have had this behavior occur simply due to a poor connection in one of the 40 (or 80) pins of the data cable to the HDD. It was fixed many times by unplugging and re-connecting a few times to clean the connector. It's free and worth a try - just don't be too rough about it!
