I was doing my first-ever Time Machine back-up tonight. I have about 130GB of data. About a half hour into it, my battery died and when I rebooted the computer from sleep mode, Time Machine said that the back-up had failed. I deleted the initial back-up in the 'Time Machine Back-Ups' folder, but it still says that I have 40GB less on my external hard drive than I actually do. My external hard drive is 300GB, so I should have 170GB left, but I only have 130GB. How do I get those GB back?! PLEASE HELP!