On April 8th, Windows XP officially becomes an ex-product. Microsoft will no longer support it, or offer security patches for it, or provide updates for its Security Essentials product running on XP. In addition, because Windows XP will no longer be an official product, other software companies will be under no obligation to support it, and it will become progressively harder to find programs and device drivers for it.
If you're still running XP, it's a good idea to think about replacing it before April 8th, or as soon as possible after. This means upgrading your PC, or at least your version of the operating system, either to 7 or to 8.1.
Check out Vic's handy story at http://www.techsupportalert.com/content/changing-windows-xp-free-help-mi... which provides details of a program that can help you migrate your files. And you can read the official Microsoft death certificate at http://www.microsoft.com/en-us/windows/enterprise/endofsupport.aspx