So your OS cant detect it, i get that much.
But what about the BIOS? I don't have a clue who your motherboard manufacturer is so i cant be certain but im guessing it would probably say what drives are connected if you go into the BIOS menu and locate 'Advanced' OR if you open the boot menu upon first loading your computer (Default key is F12) and select hard disks, you might be able to locate them in there.
The thing is, and im pretty certain this is only windows Vista +, you now basically need to tell your computer to manually assign drive letters to any hard disks that arent automatically detected and added -- with my 2 weeks experience of W7, i noted that this is probably all drives over about 64GiB but dont hold me to that.
So when windows boots; hit Start=>Right Click My Computer=>Hit Manage (You might need to give UAC permition, dunno)=>Storage=>Disk Management(Patience, its slow to connect to the virtual disk service sometimes)=>Select the disk you wish to enable at the bottom, right click the partition you wish to enable (Most people only have one partition set up on the drive in the first place) and hit either Assign Drive Letter or Change Drive Letter And Paths.
Goodluck, hope this helped, it might not be right because that was entirely off the top of my head but im hoping thats what you were after.
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