I have an external HDD that works on any other machine I test it on, except mine. It was previously working and recently I needed to use it and it didn't work. It appears in device manager, not in disk management. A drive letter might not be assigned to it, although I can't see it in disk management to assign a drive letter to it.
If device manager shows it without any errors, hop over to disk management and force a rescan/refresh. IT should show up here. FYI, you can't assign a drive letter to a drive, just to a partition on the drive.
The problem is you most properbly have a few drive letters and the hdd is trying to use one that is already taken, go into computer manager and change the cd drive letter to z or manually give the external hdd a drive letter, it will then pick this letter up every time you plug it into the offending laptop/pc
may be for win version. u can promt drive latter . go= control panel> amdimintrativ tools>computer managementdisk management>right button click on ur "no name HHD" & select change drive latter & paths & give all informatioin