After supporting Windows XP for a really long time, Blender foundation decided to drop the support for it in release 2.77. The reason for taking such a decision was the switch to Python 3.5 which comes with PEP 11 which does not support little-used the platform (includes Windows XP).
Microsoft had dropped support for Windows XP, before the release of Python 3.5, which ended up with Python 3.5 not supporting XP. While there are possibilities to backport Python 3.5 to XP, it does not seem like Blender offers support after backports are developed.
This means Blender 2.77 32 Bit release will require Vista or higher release of Windows. While this might be bad news for XP users, you can still continue using 2.76 release, which is the last and latest version of Blender to support XP.
You can find the official details from this mailing list Thank you for reading, If you have any questions leave a comment below.
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