Probably because both HDD's did'nt "catch" and attempt to respond to the same "signal". Working/not working can be real sporatic.

Hmm, ok. Well I'll try setting to cable select and try again when I get home. Thanks G

If that happened to me and I was like well I haven't backed up my stuff in a long time I probably would've if I was able to get back to the desktop just in case it really does go out.........just food for thought

You would've what? Reformatted?

Pyrobob83,

have you ever uninstalled the henrik's program?

this is a long shot: did you check your cmos battery ?

just a suggestion

Which one of Henrik's programs? The only one I've uninstalled was that demo program that you had to install to get his temp monitoring program to work. But that was a while ago - well before messing with adding another HD.

And I've never understood anything about the CMOS battery - Don't know where it is or what it does.

Yikes... After monitoring my temps using Hankos program, I turned the acpiec back on and shut down. When I turned it back on... I got "Operating System Not Found" So I turned it off, and back on again and things were working. What could've caused this?

----------> this is what you said in the beginning and i follow the rest and i found no where that shown you uninstalled it.

cmos battery is keeping your bios info. if it starts loosing its power that sometimes it keeps your configurations and your machine runs ok and sometimes it forgets and does not keep your configurations and your machine runs like ..
where is it? in my machine it is under the hard drive.

Thanks dude. Yeah, I'm guessing the events these past few days had nothing to do with uninstalling that program. I'm convinced it's a bad drive and so every time I put it in, it "resulted in such a serious system conflict that the operating system is unable to boot" (users manual) and hence reset the Primary Master to [NONE]. Perhaps what caused this the first time was messing with the acpiec - I'm not really sure.

And thanks for the info on CMOS. I suppose this could be the problem, but I somehow doubt it. If it happens again with the replacement drive, I'll make sure to research it.

Well, G, you were right (I think). I set the jumpers to 'cable select', plugged it back in and altough it still did reset the Primary Master to [NONE], resetting the configuration settings in the bios allowed me to boot, whereas before I didn't. So I was able to get what little data I had on the drive off before pulling it out and packing it up to be RMA'd.