The clicking noise is your harddrive. The same happened to my Ipod, it wouldn't turn on and would simply make a clicking noise while trying to start. The rest of your machine may be fine. It is hard to tell. Can you extract the harddrive in anyway and try to attach it with IDE-to-USB cable to another machine to see if it is working?
Edit - Although I have heard of cases where the PSU may make a clicking noise, did you pinpoint where the noise was coming from? Hopefully it is your PSU, as you will be able to salvage your HDD if that is the case.
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