I can't say for certain, but try it with another drive if possible.

I've seen some amazing IDE failures.  Many years ago, the little IDE card 
(remember when you needed a seperate one?) in my 486 died.  When powered, the 
innocent (blamed anyway) 120Mb drive kept spinning up and down.  You could see 
how heavily it was draining the power by the dimming of the front panel lamps!