My home computer has Windows 7 Ultimate, x86. I downloaded and attempted to start every version of SQL Server 2012 for x86 OS, but they all gave the "SQL server media not supported on a X86 system. To continue, run the SQL server setup media that matches your system" error when I attempted to run the setup file.

I believe you are trying to install 64 bit SQL Server on 32 bit desktop. Please Download 32 bit installation files.

Also check

Hardware and Software Requirements for Installing SQL Server 2012

Supported Operating System

Windows 7, Windows Server 2008 R2, Windows Server 2008 Service Pack 2, Windows Vista Service Pack 2

• 32-bit systems
  • Computer with Intel or compatible 1GHz or faster processor (2 GHz or faster is recommended.)

• Proposed as answer by Lydia ZhangMicrosoft contingent staff, Moderator 4 hours 35 minutes ago

In Add/Remove Programs, click "Microsoft SQL Server 2012 Setup" and click Repair.

http://www.sqlservercentral.com/Forums/Topic1424017-2799-1.aspx

https://connect.microsoft.com/SQLServer/feedback/details/675311/misleading-error-message-when-installing-sql-server-08-r2-express-on-win7-with-sql-already-installed-in-winxp-mode

 I donot have Microsoft SQL Server XXXX  Setup

• Edited by debian113 1 hour 34 minutes ago