Western Digital 120 GB Model WD1200U017.002 SN WXE0o6620867

If you have alcohol 120 installed, uninstall it first.
Now Right click on my Computer - Select Properties - Hardwaredevices - Device Manage: Check your DVD/CD drives. Whether everything is connected.
Good Luck.

For Windows:
Plug the external drive into your main computer. Open up My Computer, Right Click on the drive, choose Format, select FAT32.

For Mac:
http://www.mac-forums.com/forums/other-hardware-peripherals/49932-formatting-external-drive-fat32.html

If you wrote zeros to the drive then there is no way of recovering the data. All you can do is format it and start over.

try to format the external HDD using command prompt..... type "cmd" in start & search box and hit enter... command prompt will be opened... Now type "format X:" where X=your external hdd drive letter.... if it does not format then right click on my computer icon> goto manage >select Disk management> select the external drive> right click and delete partition > again right click and select create partition > again right click and select Format drive.....
this will fix the issue....

you may have a FAT32/NTFS format problem between your wd500 and your pc. or differently formatted partitions. right click on their device letters on 'my computer' and look at 'properties'. should tell you how they're formatted and # of partitions, etc.
just a guess!
good luck!

Go to your control panel and then administrative tools, select Computer Management.

Now select Disk Management and expand the window.

Your drive should be listed here, if not then you need to check your computer hardware has not got any issues before proceeding.

If your drive is listed and says healthy then right click on it an select Properties,

In here you can delete partitions.

Delete the last one first

Now delete the first one.

Now right click the drive and select Format. Choose NTFS as the file system and do not tick any boxes you do NOT want quick format. Again start and let it do its thing. When it is done restart your computer and you should be good to go.

Try putting it on another computer. Try changing out the usb cable. If you are in windows, you can:
Go to - Control Panel\Administrative Tools\computer management
Then go to the storage section, and click on disk management. Does the drive show up there? (It may not have a drive letter). If that is the case, it may not be setup correctly, or lost its fat table.. you can assign drive letters here as well as format as needed.

Click Properties, and check formatting. I had one of those, and it was FAT32, so it will only except a a certain size of files. All you need to do is right click on it and select format. This could take a while.

With the drive plugged in, go to My Computer, and right click on your drive. Select Properties from the menu, and click on the Autoplay tab. Click on the "Select Action to Perform..." and select "Take No Action" from the menu. That should stop Windows from ever asking you what to do with the drive in the future.

I think the MS PRO portion is for a card reader for formating a memory stick if you have one, if not don't worry.