Alright try this
1. Press [Windows], enter [diskmgmt.msc] and hit [enter] to open the Disk Management interface in Windows
2. Now You can see all the hard drives and partitions of the computer system.
3. Select the partition which don,t have the Drive Letter.
4. Right Click on that Drive and Select “Change Drive Letter and Paths”
5. Now click the Add button and assign a drive letter to the partition.
6.After this your Missing Drive is Visible in Your Windows 7 Computer.
hope this helps