First make sure it's not just a drive letter issue. Sometimes Windows forgets to assign a drive letter when you plug in an external drive and you then have to assign one yourself.
Go into Disk Management:
Control Panel > Admin Tools > Computer Management > Disk Management
In the bottom-right panel showing the drive ribbons, look for the ribbon which represents your external Toshiba.
It will have no drive letter and will be labelled as "Raw" with no drive name.
Right-click that ribbon and choose "Change Drive Letter & Paths".
Click "Add".
Choose a letter.
Click 'OK' and wait for the drive letter to be assigned to that drive.