If you've got any older DOS 5.0, 6.0, or Win98 boot floppies laying around, I have something that might be able to help. I've used it with great success and it can't hurt even if it does not help.
Boot up on one of these older boot floppies, and do a dir on it to see if "fdisk.exe" is on it. If it is, try this command: "fdisk /mbr". When you hit enter there will be a brief pause and hopefully, you will go quietly back to a command prompt. If the drive has a problem you might get an error. If you got no output at all, it worked. This command overwrites the first 34 blocks on the disk that contain the media descriptor file, and a few other pointers and such, but none of the actual data on the disk. It can not cause a problem, since this data is always the same on any system with a standard BIOS chip. Sometimes it gets corrupted, and the system will just flat out not try to use the drive. There's no error message because the OS has no idea that the disk exists - it is "turned off" before the machine ever tries to load the OS.
S.M.A.R.T is a piece of software on the disk drive's controller card that monitors bad blocks and other statistics. The data can be used by the controller and software in the PC to predict failures if it is turned on. If the diagnostic SW says "failed Read" when testing S.M.A.R.T., then either the drive itself is not responding to the test, the drive can't read the statistics from it's own memory, or S.M.A.R.T. is disabled (usually a jumper on the drive). If the drive has a jumper to do so, disable it. Then go into the BIOS setup on your PC, and disable it there, too. That will rule out S.M.A.R.T. as the problem.
Do yourself a favor - try a different ribbon cable before you knock yourself out too much. They do go bad for no apparent reason and most people never suspect them.
