Sounds like the HDD is having a power problem when it tries to spool up to full speed which = dead HDD. Chico is right then it will be pricey to salvage any data.

Get into a RAID setup and you'll never have to worry about your data again. I have 3 of these setup in RAID 5. I keep a spare to swap in whenever an HDD croaks (hasn't yet). I have an external controller that I use for the RAID 5 array, but that card uses a 64 bit PCI-X slot and a lot of MB's don't have one. So you will need to find an equivalent for your MB. I have a separate HDD for my OS and programs (setup in RAID 0 from an on board controller), that I Ghost to DVD-R every 3 or 4 months just to keep my windows updates close to current.