Hello,
You are in trouble. Question is if the hard drive had a mechanical failure, or a logical/OS failure.
If you heard grinding, clicking, creepy noises, you are probably having a mechanical failure. Get the pocket book, and start looking at a service to recover your data in a clean room. Off the top of my head, $400 or so.
If you are looking at a software failure (cannot boot windows/linux/mac, blue screen, no screen), then there is a chance that you can slave the (assuming IDE) drive inside of another computer. You will have to track down a converter, and go inside the machine, and wire it in. Will need to probably move a jumper from master to slave. But if this works, there is a chance that you can copy the files from one drive to another.
In the end though, you have learned the motivation of keeping backups. Burn a disk once a week. Or have a server, and have that burn on a weekly basis. Some of us backup people go so far as tapes at the home system, or do what I do... have my servers backup to hard disks on other servers.
Good luck with your situation,
Christian