Question: Cannot detect one of my hard drives. I have two hard drives and both of them are on separate IDE cables, one hard drive has the OS and is the primary hard drive. The drive was working properly but suddenly disappeared. The device manager says all hardware is working properly.
Answer: I would begin by checking your cables and jumpers. Make sure the cable is secured on the drive and on the motherboard and make sure the power cable is working. You can even swap it with the other drive or CDROM so that you know that particular power cable is working. Also make sure the jumpers are set correctly on the drive.
Next I would go into the BIOS and make sure it is seen by the computer itself. If its not there then Windows will not be able to see it either. If that's the case I would replace the IDE cable, try attaching it on the cable with the other drive (check the jumpers too) or try the drive in another computer to see if its the drive itself.
If it is seen in the BIOS then I would go to Disk Management within Windows and have it scan for the drive. It may be listed there as a foreign drive that you may be able to import. To get to Disk Management, right click My Computer and select Manage. From there you will see the Drive Management icon to view your installed drives.