The ability of the CMOS to recognize the drive is determined by the drive's electronic board. Other issues on a computer may cause the cmos to not recognize the drive, but those factors were ruled out in this case given the following:
1) The drive is not recognized by the cmos in another computer.
2) A new replacement drive is recognized and performs correctly.
As such, it's technically correct to conclude that the drive's electronic board is defective. If the board is replaced, the drive should be recognized. If then the files are not visible, the drive has suffered a physical failure as well as an electronic failure. That scenerio is highly unlikey given:
1) Physical failure of a hd normally produces clicking or grinding sounds. Note that the poster is aware of this and made a point of mentioning that the drive sounded normal.
2) The chances of a hd having both an electronic failure and a physical failure is remote at best.
Call it as you will.
I call it logic, experience, and deductive reasoning.