My hard drive does a clicking sound

What?s going on: Your hard drive is suffering from read errors. It?s going to a spot on the hard drive to read some information it needs and can?t read it. Once that happens the built-in procedure is for the hard drive controller to put the read heads back into the home position (the clicking noise you hear) and go back out to the section it couldn?t read before. It will continue to do this a set number of times and then usually give you a read error or a blue screen of death. What to do: -You can try reformatting your hard drive in the attempt to get the operating system to block out the sectors it can?t read. Sounds nice in theory, however, if you have bad sectors developing others will probably follow which means you?ll have the same problem again. If money is a serious issue you can try this but chances are this will only be a temporary fix. -Replace the hard drive and reinstall your operating system. At $80 this is likely to be your best option if stability is your primary concern. Let us know if you have any other questions and please don?t forget to rate this post.

Most likely it has degrading heads. This site should help you diagnose the problem.
And definitely you shouldn't store any valuable data on it.