well, if you've replaced the drive and it's doing the same thing, there're only a few possibilities left.
1. Bad IDE cable. You may wanna try to switching it out... you've probably got one to a cd-rom...just use that temporarily.
2. Bad jumper settings on the back of the drive. It'll need to be either slave or master, depending. Make sure it's set right. Also, some drives have 'master with slave' and 'master without slave' settings. If you need more info on this, lemme know.
3. Bad IDE controller. If this is the case, you're out of luck. Basically a part of the motherboard died... there's no way to fix it except to buy a new motherboard. That's really not as bad as it may sound... you can get a brand new motherboard for as little as $60. But it still sucks.
Anyway, that's pretty much all I can think of.