Sometimes, .NET Framework errors can cause issues in the Windows environment. Follow these steps to uninstall and re-install .NET Framework.
Run => appwiz.cpl => uninstall all “.NET” related programs from your computer.
Run the .NET removal tool found here
Reboot the computer.
Re-install from the lowest version on up. For many systems, just run the full version of 3.5 and then install v4 and so on.