Mishandled,
Your best bet would be to remove the Hard Drive from your Dad's computer and put it in your computer. (I pull the ribbon off my optical drive and let it use that ribbon and power.) Then boot up your computer normally. Then remove all the data from your Dad's Hard Drive so you have a copy of it on your computer's Hard Drive.
Then you are free to wipe out the drive and do a fresh install of the OS from the CABs back in your Dad's computer.
Take Care,
Richard