EDIT: argh maineman was faster
Welcome to the forum
Providing that the HDD is not damaged, my suggestion is to install the HDD into an external box so you can access the disc contents and recover all files you need. Alternatively, you can install the HDD into another computer, and again recover all files.
Another option is trying to boot the computer with a LiveCD of a Linux distribution like Ubuntu or Knoppix. After the boot, you can recover all files from the HDD and save them into another HDD (an external disc or an USB pendrive for example).
If the HDD is damaged, the only solution is to ask a specialized company to recover data from the disc. This is a very costly option however