Troubleshooting Installation Issues with .NET Framework 3.5 on Windows Server 2012

To address installation issues of .NET Framework 3.5 on Windows Server 2012, follow these detailed steps:

1. Verify the .NET Framework 3.5 installation status: Launch Server Manager, access the 'Add Roles and Features' wizard, and confirm if .NET Framework 3.5 is installed. If present, consider a fresh installation by first uninstalling and then reinstalling.
2. Execute the DISM tool: Access Command Prompt with administrative privileges and input: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs (substitute 'D:' with the appropriate drive letter of your installation media). This facilitates .NET Framework 3.5 setup using your media.
3. Consult Windows Update: Navigate to Windows Update settings, perform a check for updates, and apply any that pertain to .NET Framework. Afterwards, attempt the .NET Framework 3.5 installation once more.
4. Adjust Group Policy settings: For domains, verify Group Policy settings concerning .NET Framework setup. Ensure the policy 'Specify settings for optional component installation and component repair' is enabled and the setting 'Download repair content and optional features directly from Windows Update instead of WSUS' is active.
5. Assess antivirus interference: Antivirus programs can obstruct the .NET Framework installation. Temporarily disable antivirus protections and try installing .NET Framework 3.5 once again.
6. Check the Windows Installer service: Confirm that the Windows Installer service is operational by checking in the Services console. If it's not active, initiate the service and proceed with the .NET Framework 3.5 installation.