Hi Joseph,
1. Does other USB device work fine on this computer?
2. Do you get any error code or error message?
3. Was the Toshiba External Hard drive working fine before with this computer?
**Method 1:**You may run the fix it from the article.
Hardware devices are not working or are not detected in Windows
http://support.microsoft.com/mats/hardware_device_problems/en-us
**Method 2:**You may assign a different drive letter and then check.
Change, add, or remove a drive letter
http://windows.microsoft.com/en-US/windows7/Change-add-or-remove-a-drive-letter
Method 3:
****a) Click **Start.**b) In the search box type **Device Manager.**c) Locate Disk drives and expand the chevron.
d) Right click **External drive.**e) Click Properties and then go to **Drivers tab.**f) Click Uninstall and click Apply and OK.
You may reinstall the drivers from the manufacturer’s website.
After reinstalling the drivers, you may select scan for hardware changes and see if the drive gets detected correctly, if it does not help then try restarting the computer.