I have a 60GB laptop hard drive that I currently have hooked up in a external hard drive case that works in the external hard drive case, but it is not recognized when I try to put it back in the laptop.

I got this 60GB drive refurbished, installed it into my laptop, installed Windows XP, and it worked perfectly. I took the old laptop drive (that I was getting a SMART drive warning of immenent hard drive failure) and put it into the external case. It also worked, though it was slow. The old drive that I was using as external started crashing, but still works. I wanted to transfer a lot of files from an old computer, so I took the new hard drive out of the laptop, plugged it in to the external drive case, and copied the files from the desktop. This is when the problems occurred.

When I went to reinstall the good drive into the laptop, it would not recognize the hard drive. I tried going into BIOS, I even tried my Windows XP installation disc, but I cannot get it to recognize the good hard drive. When I plug the good hard drive back into the external case, I can still use it as an external drive with my desktop without any problems.

I tried installing the old drive, the one that is failing, and the laptop recognizes it, warns me of immenant drive failure, and lets me start trying to install the operating system onto it (I had formatted it when I turned the old drive into an external drive), but then the old drive crashes.

Why would the laptop recognize the defective drive but not the other one?

Is the drive getting power in the computer first of all?