Does the computer still give you a "device connected" tone when you plug in the external drive?
If yes, it may just need a drive letter assigning to it, a common problem with external hard drives, especially if that hard drive is not frequently used with that computer.
Open Disk Management: Control Panel > Admin Tools > Computer Management > Disk Management.
Concentrate on the bottom-right panel showing ribbons which represent each detected drive.
Find the ribbon which relates to your Toshiba drive, it won't have a name and will have "Raw" as the description.
Right-click on that ribbon and choose "Change Drive Letter & Paths".
Accept the default letter or choose a different one from the drop-down list.
Click 'OK' and wait for the ribbon description to update itself.