DOTNETFX 3.5 is a prerequisite for the installation of ArcGIS. However, Windows 10 does not install it by default. In the ASCTech environment, if you try to install it in the prescribed manner (Control Panel -> Programs and Features -> Turn Windows Features On and Off) an error message occurs stating the the installation failed. This is likely due to the fact that ASCTech modifies group policy to point Windows to our own update server rather than to Microsoft’s servers.
The solution is to install DOTNETFX 3.5 from installation media, such as a Windows 10 disc or a USB Flash drive that contains the installation files. To do so, insert the media containing the installation files, open a command prompt as an administrator, then use the following DISM command:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:[Drive]:\sources\sxs
(Please note that [Drive] will be the media’s drive letter)
Once the process is complete you may install ArcGIS accordingly.