Over time, Windows loses stability. If you keep a computer for more than two years, at some point you're going to have to bite the bullet and reinstall Windows from scratch. But contrary to popular belief, you won't have to reformat your hard drive. The bad stuff you need to get rid of is all in your Windows folder.

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.