External USB hard drives don't work with Windows 7, but with Windows XP
On a machine, WITH dual-boot Windows XP and Windows 7 (both 32-bit) OR Window Vista.
Several external hard drives work well under Windows XP, but under Windows 7 none of them is shown as a drive in Explorer.(VICE-VERSA)
Solution
Right click on Computer > Manage > Disk Management(under Storage Option)
If the drive is showing there, assign a drive letter
