Today I got my replacement HDD, Seagate Barracuda 500GB Sata2 drive, after it died 10 days ago taking away a lot of my multimedia.
Well, this is not the first time it happens to me, it's a 3rd drive that I lost on different PC configurations.
The first one died in the same scenario, 7years ago on my first PC, it was some 8GB drive, I put my PC to sleep and when I tried to get it back up the HDD led was on, but there was no response from the system, I restarted the PC, and there it wasn't, BIOS would not recognize the drive...
I don't remember quite how my 2nd HDD died...
What could be causing this, electricity perhaps?
Help, I don't want to lose more drives.

No one can gaurantee (outside warranty of course) that a HardDrive will not fail

This is why it's best to always make external backups (CD\DVD\Flash Drive\External HardDrive...)

There are a number of reasons why HardDrives can fail:
Heavy usage
Faulty Drive
Age of HardDrive
Power Surges
Incorrectly configured
Physical drops or knocks

The list goes on..