Backing up is an extremely important practice and it is not just a magic wand to be waved when things go wrong. A computer system may be divided into two essential parts - software and user data and an efficient and resilient system will maintain separate environments for each of these - as either physical or logical separate drives. Typically drive C will contain the operating system, installed applications and associated system files. All user data should be stored on a separate drive or partition. The system drive should be backed up using drive imaging software and I strongly recommend Acronis True Image for this purpose. It is not free, but nor is it expensive and it can recover your entire operating system and install...