Microsoft introduced WGA when Vista was launched. For those who are not aware of what WGA is all about. WGA is a mechanism used by Microsoft to detect pirated and non-genuine installations of Windows but as all Microsoft product it also has a problem which is while it’s been good at detecting non-genuine installs of Windows, it can sometimes incorrectly flag a genuine install as non-genuine and sorting this out can be tedious and time consuming and even Microsoft tech support acknowledges that WGA can sometimes be wrong.
Microsoft would be starting on WGA notification for Windows XP. Read this. Update to WGA Notifications for Windows XP Professional. As a quote from the Article
Starting this week, we will begin deployment of the latest version of WGA Notifications for Windows XP. In addition to the usual updates to validation that improve WGA's ability to detect the latest stolen or fake product keys and other attempts to circumvent product activation, this release will also include a couple of other significant updates.
Simplifying the installation and making it easy to stay up-to-date
Now what does this would mean is instead of having the Windows to stop working completely we would see black screen of hell
Which means that your XP would be working as normal but you would always see this when you open your Desktop.
As well as constanly remind you about your non-genuine version of XP