In order to repair a hard drive, you must first determine the problem. If the problem is missing files, which affects booting, then you can run Windows repair to replace the missing files. However, there are times when the drive has to be completely reformatted. If this is the case and you have valuable information on the drive, you can install a second hard drive and install the operating system on the new drive. Then install the second (bad) drive as a slave. By doing this, you are able to retrieve important documents and transfer them to the new drive. Once you have retrieved all the data, you can simply reformat the drive from within Windows.