#1 - Nov. 14, 2013, 10:44 a.m.
Blizzard Post
We’re aware of an issue that began after the 12/11 Battle.net update; certain versions of Windows XP are unable to start up the Battle.net Agent to run Blizzard games.

To resolve this issue, you must manually uninstall ALL Battle.net related files, including the Battle.net Desktop Application. Follow these steps:

1. Show hidden files and folders.
2. Using Windows Explorer, delete the following folders:
C:\Program Files\Battle.net
C:\Documents and Settings\All Users\Application Data\Battle.net
3. Choose the appropriate option for the launcher you use:
  • Battle.net Desktop Application & Hearthstone users: Use the updated Battle.net or Hearthstone installer on the Battle.net Games Management page to reinstall Battle.net application and related files.
  • Classic launcher users: Launch the game using the normal shortcut to download the updated Battle.net/Agent files.