Windows Plug and Play
If your drive isn't detected, there is no need to panic. Both Windows Vista and Windows 7 is a little funny about this sort of thing, but it is quite easy to fix. The problem is that the drive is not initialized, so the standard plug-and-play procedure for adding a drive does not apply. First, you must initialize the drive, then it will allow you to format it. After the drive has been formatted, it will be ready to use.
The first thing you need to do is go into the Control Panel, then double click on Administrative Tools. After that, open up Computer Management, then go to Storage, then Disk Management. This is where you will see all of your drives listed. Be extremely careful in this section because you don’t want to screw up your main hard drive.
What you are looking for in the Disk Management area is your new hard drive. If you only have one hard drive, it should show up as Disk 0. Therefore, your new drive should most likely be Disk 1. Underneath the name Disk 1 it should say Unknown, the size of the disk, and Not Initialized. Right click in this area and you should get a pop-up window. Click Initialize Disk and it should only take a couple of seconds.
Your hard drive is now ready to be formatted.