Download the Powermax diagnostics, this should tell you what is wrong.

Believe it or not freezing your hard disk has worked for some, although I have not tried it.

Here are 200 ways to revive a hard drive(PDF)

I've heard of the freezer trick working, but it didn't for me the one time I tried it. I think it's mainly for a drive that won't spin though. If you want to try it, it shouldn't hurt anything as long as you put it in a plastic bag first.

If it does work, be prepared to backup everything as quickly as possible because it may not last long.

If that trick doesn't work, or you decide not to try it, to get your data back you can try hooking the drive up as a slave in a working computer and and see if you can access the files you want.

If you still can't see them, try this program:
http://www.snapfiles.com/get/restoration.html
It'll take awhile to recover a bazillion files, but if they're important, it may be worth the time. In the future, remember to backup often

Backup! backup! backup! And then backup again!

Freezing won't work unless the drive des NOT spin. Motor bearing failure is the most common hard drive failure mode.

There could be a few things to try:

1. Your BIOS might have been zxnrbled (or virused) to the point where it thinks the wrong drive is there.

2. Your disk controller chip on the computer motherboard or accessory card may have failed.

3. The drive selection jumper may have fallen off the drive. In this case, two devices may have the same address. If so, they will fight over the right to have that address instead of working.

4. Check the cables. If the data cable is upside down, or if one or more pins is disconnected from the cable, it won't work.

5. Your virus checker may have quarrantined the disk.

6. If you had a power failure, the damage might be restricted to the partition table, the timing marks, or the directory. Norton makes tools for unzxnrbling those.

7. If a worm got your hard drive, it's probably all blank.

8. If it made a loud screee when it failed, a headcrash occurred. It would take a disk drive manufacturer's tech in a clean room with a bunch of spare parts just to see if anything is left. Got a couple of kilobucks to spare?

9. If it's going bang-bang-bang, or if it sounds like a maraca if youi turn it upside down, the bakelite disk platter shattered. Bye bye drive.

10. If the circuit board on the drive failed, that can be replaced at a cost.

11. The drive may have been exposed to a strong magnetic field (such as the permanent magnet in a subwoofer).

If only the data have been erased, the drive can still be reclaimed by reformatting it.