You are talking about a couple different parts here... is the computer dead (as in wont power on) or does it come on and not boot (as in hard rive is making funny noise or no HDD found error message)
If the machine is dead, most likely, you havent lost anything from the hard drive.
If the hard drive is dead, then you have to pay for a service to recover the data. There are software packages that will do low level data recovery but I do not have any experience with them.
Can you be a little more specific in what it does when you turn it on?