How to Reinstall Windows Without Losing Your Data – [PC World] Before you begin, gather your Windows and application CD-ROMs. Back up your data files (just to be safe), and then clear two days off your calendar. If everything goes smoothly, you can reinstall Windows in a few hours. But you have to assume something will go wrong: You may not be able to find a necessary CD, or data won’t be where you thought it was, or something will simply refuse to work. There’s a difference between a repair reinstall and a complete reinstall. Though a repair (also called a refresh) will let you keep your current settings, a complete reinstall will give you a truly fresh version of Windows. Repairs are fast and easy, but they don’t fix anywhere near as many problems. The instructions below are for total reinstalls, except where noted.