Hi, I have an external hard drive GHD225U40 that

First, connect your GHD225U40 to your Win 7 computer and then check the Device Manager. Go to Universal Serial Bus Controllers and expand it.
Count the USB Mass Storage Device that appears in your Device Manager.

Then, without closing the Device Manager, safely remove the HD from your Win 7, and wait for the Device Manager to refresh. Count again the Mass Storage Device. If one of the mass storage devices disappeared, then your HD is being detected by your Win 7.

The next thing that you need to do is to try changing the drive letter of your HD.

While it's connected to the Win 7, follow the steps below:

- Right-click the "Computer" icon on your Desktop screen.
- Select "Manage", then click on "Disk Management".
- Check the drives that will appear in your Disk Management.
- If there's a drive that has almost 40GB capacity, and if it does not have a drive letter assigned to it, right-click on it > select "Change Drive Letter".
- You may select starting from Z to G. Do not assign a drive letter that's in the beginning of the alphabet (like D, E, F), because computers usually use these drive letters. So using the Z, Y, or X is the safest way.

If same problem occur after changing the drive letter, check the status of the HD under the Disk Management. The HD should be healthy.

If not, I would suggest to back-up all the files from the HD to your Win XP computer, then reformat the HD using your Win 7, so that it will work with both computers.

Thank you and good luck!

Go to device manager on computer, (while the external hardrive is connected) find the drive on the list and right click it or somthing, and look to see if you can update any drivers on it..this is more then likely your problom because when you switched from xp to 7 it might have wiped out the drivers for the external hardrive