Can't install .NET Framework

If you came across a situation when your computer is broken and you can't install or update .NET Framework, you need to get the .NET fx Cleanup Tool.

This .NET Framework cleanup tool is designed to automatically perform a set of steps to remove selected versions of the .NET Framework from a computer.  It will remove files, directories, registry keys and values and Windows Installer product registration information for the .NET Framework.  The tool is intended primarily to return your system to a known (relatively clean) state in case you are encountering .NET Framework installation, uninstallation, repair or patching errors so that you can try to install again.

More details and download here: Aaron Stebner's WebLog : .NET Framework Cleanup Tool User's Guide
Alternate download here: Download .NET Framework Cleanup Tool 6.0.3790 - It will remove files, directories, registry keys and values and Windows Installer product registration information for the .NET Framework. - Softpedia