I am no expert. Here's a few questions that might

help provide some basic information for diagnosis:

Under what circustance did the hard drive go dead? Was it all of a sudden while in use, or was it when you try to boot it up following a previous shut-down?

Is the hard drive internal or external?

Does the hard drive status light come on when you power on the computer? What appears on the screen at that point?

Disconnect all USB or firewire devices while the power is off. Leave only the keyboard and mouse. The power it on. What happens now?

If the hard drive is external, try it on another computer.

Hard drives these days are fairly robust. The chances of the drive going bad physically is slim. Most of the problems are due to device conflict, or lost of partion tables, etc.