Well... First don't format it or do anything that will write to it.
A lot of things can cause this problem -- if it's a hardware issue, then you are in more trouble, if it's just corrupted data, then you may be able to save it yourself with software.
Hard drives make a sound when they power up. It's the sound of a physical disk starting to spin. If you don't hear the usual "whirr", then it's probably a hardware problem. If it makes a bunch of unusually loud tick sounds, then I'd guess it's a hardware problem in that case too.
I know this all sounds very unscientific, but it's my experience with bad HDD's.
If you think the hardware is working fine, then I'd look into using software to try to recover the data. There are a lot of options. I've used a program called "Get Data Back" several times in the past with success. There are other alternatives too. Try google. Also, there are some linux live cd's aimed at data recovery (though there's a bit of a learning curve for some of the tools.) Otherwise, you can pay someone for data recovery, but from what I've seen, it's surprisingly expensive.
I'd try the software tools, hope for the best, and be prepared to put a bit of time into it if you're lucky enough to be able to recover at all. If you’re not up to all this, you could send me a private message and we could probably work out a deal for you to mail me the disk and I’ll do my best to recover your data.