I googled a few hours but couldn't find answer so I decided to ask for help here. Any input or insight would be much appreciated. I just migrated my old 100GB C drive to a new 300GB one. Now I want to use the old 100GB as my storage drive, so I put it in the internal hard disk bay in my ThinkPad T42 CD Drive Bay. But Windows does not recognize it no matter what I do. I tried 2.5 inch ATA-to-USB adaptor cable to no avail. I have tried both method many times in the past and they usually recognize drives immediately. No need to set drive letters or jumpers. The only difference this time is that this drive used to be a bootable C drive. When I connect the drive, Windows says "New Hardware Found" and starts installing. But toward the end, it says "Unknown error occurred and drive might not work properly". Sometimes it says "Your device is installed and ready for use". In any case, if I right-click My Computer -- Manage -- Storage -- Disk Management, this drive is not listed there. If I go to Device Manager -- Disk drives, this drive is listed there. Its Properties says "This device is working properly". And the Location says 0 (0), which is the same as the new 300GB C drive. Is this why I am having this problem? After many failed trials, I put the old drive back to the main drive bay and Windows started fine just like before. So the old drive itself is fine. It's just not recognized. So I rebooted with Windows OS Installation Disk and formatted this drive with NTFS. Then, using EASEUS Partition Master Home Edition, I tried to create partitions but it fails to do so. Acronis True Image Home (Add New Disk) does not find the drive. Just to test, I took the C drive out of my other laptop (ThinkPad T40) and tried the same thing and it did not work either. So drives that are (used to be) bootable C cannot be recognized or partitioned? Is there anything I can do to use this drive? In Summary: Device Manager (Disk Drives) recognizes it Disk Management does not recognize it EASEUS finds it but fails to partition Acronis does not find it Both 300GB and 100GB have Location of 0 (0). Thank you for your help.