The Device Manager displays a yellow ! icon next to my external drive

It is always a good idea first to check Windows Disk Management before the Device Manager.

1. Right-click on (My) Computer.

2. Click on Manage.

3. Choose Disk Management from the left column.

4. Try to find the external drive in the lower window. It should be "Disk 1" or some other number (but not Disk 0).

5. If it is displayed there, you can troubleshoot it inside the Disk Management (see Windows section). If not, continue on.

6. Then choose Device Manager from the left column.

7. Choose Disk drives.

8. If the drive is not seen there, check under Universal Serial Bus Controllers (if the drive is connected via USB). The drive should appear as a USB Mass Storage Device.

9. If a yellow ! icon is displayed next to it, double-click on the drive.

10. A Properties window will appear and will probably say "This device is not working properly" and will give either (Code 28) or (Code 10).

11. If Code 10 appears, the drive has most probably failed. Verify by trying the drive with another USB cable or port, or on another computer.
    If the drive does not work on the 2nd computer, the drive is probably defective. You can begin a replacement request at our Warranty Services Page.

12. If Code 28 appears, you will need to test the drive on another computer.

13. If the drive functions correctly on another computer, the Windows USB drivers are corrupted or missing. You will need to try to reload the USB drivers for the operating system by inserting your Windows install CD, rebooting, and attempting a Repair/Restore.
    This can be dangerous to your data and you should disconnect your external drive before attempting this.
    If the drive does not function correctly on the 2nd computer, it is probably defective. You can begin a warranty replacement at our Warranty Services Page.
    
    For Vista and Windows 7 Only: If the drive works fine on another computer, there are a few steps to follow while the drive is connected to the original computer:

14. 1. Right-click on Computer and choose Manage.

    2. Double-click on the Device Manager.

    3. The device will usually appear under "Other Devices" or "Unknown Devices"; right-click on it and choose Uninstall.

    4. Once it has disappeared from the Device Manager, disconnect the device.

    5. Open a Windows Explorer window (right-click on Start > Explore).

    6. In the address bar, type c:\windows\inf and press Enter. For Windows 7 type c:\windows\system32\driverstore and press Enter.

    7. Delete the file INFCACHE.1.

    8. If you get an error when trying to delete this file, try the following steps:

       1. Right-click on INFCACHE.1.

       2. Select Properties.

       3. Click on the Security tab.

       4. Click Edit to edit permissions.

       5. Click Add to add Group or User name.

       6. Click on the user name under which you are currently logged in.

       7. Click on the Full Control box in the lower permissions section, then click OK.

       8. Delete the file.

       9. Reboot and reconnect the drive. The file should be rebuilt, correcting the problem.

       10. If that fails, you will need to try to reload the USB drivers for the operating system by inserting your Vista install CD, rebooting, and attempting a Repair/Restore.
           This can be dangerous to your data and you should disconnect your external drive before attempting this.