How to solve the error code 0x800f0928: Windows couldn't install .NET Framework 3.5 in Windows Server 2012

There are several steps you can take to solve the error code 0x800f0928 when trying to install .NET Framework 3.5 in Windows Server 2012:

1. Check if the .NET Framework 3.5 feature is already installed: Open the Server Manager and go to the "Add Roles and Features" wizard. Check if the .NET Framework 3.5 feature is already installed. If it is, try repairing it.
2. Use the DISM command: Open the Command Prompt as an administrator and run the following command: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs (replace "D:" with the drive letter of your Windows Server 2012 installation media). This command will install the .NET Framework 3.5 feature from the installation media.
3. Use the Windows Update: Go to the Windows Update settings and check for updates. If there are any updates related to the .NET Framework, install them and try installing the .NET Framework 3.5 again.
4. Check the Group Policy settings: If your Windows Server 2012 is part of a domain, check the Group Policy settings related to the .NET Framework installation. Make sure that the "Specify settings for optional component installation and component repair" policy is set to "Enabled" and the "Download repair content and optional features directly from Windows Update instead of Windows Server Update Services (WSUS)" policy is set to "Enabled".
5. Check the antivirus software: Some antivirus software may interfere with the .NET Framework installation. Try disabling the antivirus software temporarily and try installing the .NET Framework 3.5 again.
6. Check the Windows Installer service: Make sure that the Windows Installer service is running. Open the Services console and check if the Windows Installer service is running. If it is not, start it and try installing the .NET Framework 3.5 again.
7. Check the system files: Use the System File Checker (SFC) tool to check for any corrupted system files. Open the Command Prompt as an administrator and run the following command: sfc /scannow. This command will scan the system files and repair any corrupted files.