Silent repair on 64 bit computer with .Net Framework version 4.0.30319 :
%windir%\Microsoft.NET\Framework64\v4.0.30319\SetupCache\Client\setup.exe /repair /x86 /x64 /ia64 /parameterfolder Client /q /norestart
%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe –i