+ 1 Votes Cabling issue by the sounds of it gechurch 1 year ago Ok, so in summary:* Both drives show up individually* Both drives showed up together, when the 500GB was set as boot drive* The 500GB doesn't show up when the smaller drive is plugged in as the boot driveThe problem is a physical one, since the drive isn't showing up in the BIOS (if it doesn't show there it is impossible for it to show up in My Computer). Since both drives can work together the problem must be with whatever cabling changes you make to "Reinstalled 180 Gig as operating system drive". There could be a few causes:* Maybe you're using a different SATA cable, and it is faulty* Maybe you're using a different power connector, and it is faulty* Some motherboards require you to use SATA ports sequentially (ie. SATA0 first, SATA1 next etc). More playing around could tell you what is going on. The quickest solution though would be to plug things back in so that both drives are detected. Now go into the BIOS setup program (usually by pressing Del or one of the function keys just after boot). In there you should be able to set the hard drive priority. Change it so that the 180GB drive is first. Now both drives should still be detected, but the BIOS will choose to boot into the OS installed on the 180GB drive instead of the 500GB drive.