I had a problem installing .NET Framework 3.5 feature on a recently reset Window 10 computer. It kept telling me that Windows couldn’t find required files to complete the requested changes with an error code 0x800F081F.
Here are 3 ways to fix this issue if it happens to you as well.
Windows Update Troubleshooter
The link “Tell me how to solve this problem” in the above screenshot takes you to a page that suggests Windows Update Troubleshooter. Download the tool and run it with local admin privilege to fix any issues you may have on your Windows 10 system that relates to Windows Update.
Make sure you always get a copy of the tool through the link above so you have a most recent one to run and fix the problem. Once done, try to enable .NET Framework 3.5 in Windows Feature to install it again.
Remove any higher version of .NET Framework
Some of the sites I searched mentioned an approach that removes the newer version of .NET Framework first before installing version 3.5. For example, uncheck .NET Framework 4.7 from Windows Feature to remove it from your system
Then, check .NET Framework 3.5 to see it passes the installation process. If so, congratulations. You should check .NET 4.7 or any higher version to install it again.
Manually install it using DISM
If the above two approaches didn’t get you through, it’s time to use DISM to manually get .NET Framework component installed right from Windows 10 installation disc.
DISM.exe (Deployment Image Servicing and Management) is a command line that can be used to service a Window image or to prepare a Windows Preinstallation Environment image. It also has the feature that allows us to install feature components manually. Open an elevated Command Prompt window and run the following command.
DISM /Online /Enable-Feature /FeatureName:NetFx3 /Source:f:\sources\sxs
You will need the Windows 10 installation disc mounted before running this command to install. You can download the official Windows 10 ISO through Media Creation Tool and mount it by right-clicking the ISO image and selecting Mount.
Once finished, you will notice that .NET Framework 3.5 option is checked next time you open Windows Features dialog window.
The DISM way saved my day at last but I hope you don’t have to get that far because it does take the time to get everything in place before I can even use the tool to fix the issue. Hope it helps.