Hi Bernie

Unless it was a hardware failure that trashed the hard drive you can use a repair disc (Vista and Windows 7) to repair most problems with the OS. (The repair files will also run from the original Windows DVD)

If you have XP, start from the Windows install disc (Assuming it runs the same service pack) and you can re-install the OS without losing any of your programs. (Just make sure you choose the repair option)

If your computer went down without damaging the HDD, and you have just bought a new computer to replace it, you can install the HDD in your new computer and set it as the boot drive then after a few re-starts to load the new drivers, everything should be up and running. (You will need to re-activate Windows with Microsoft; however it is painless and uses a Freephone number, full instructions will appear on-screen when you select the activation option)

You cannot run an OS from a USB 2 dock, however if it is an eSATA or USB 3 dock then you can.

Hope this helps

Bill