is it a new drive? if it is you might have to format it. Go to right click on my computer and select manage. Then go to disk management. You should see the drive there and you will be able to format it. You should also check the device manager to see if the drive shows up. Right click on my computer and select device manager. If you see a little error message over a usb mass storage device you have a driver problem. If you don't see it try unplugging and plugging it back in while the device manager is open to see if it shows up.
