And how could you know that your windows is running? Isnt that when your HDD is off, OS is not running.
I have a Quantum HDD. Similar to ur problem but it happened very different. After I have slot in my little brothers primary school CD into the CD-ROM, suddenly a blank screen appears and when I CTRL-ALT delete later, I then receive a blue screen. I saw the word "KERNEL error..." something like that and the whole thing (HDD etc) turned completely OFF immediately. I can't turn it back on at all but I could hear that my HDD tries to run during system check. Then after about 4-5 seconds, the HDD turned OFF again.
I have made a thread of this one. Some say its virus. I do believe that the data in there is still safe. Maybe it has got something to do with the motor inside that needs to be repaired.