When compiling UE4.10. "GenerateProjectFiles ERROR: We couldn't find a valid installation of Visual Studio."

Hey ytianlong-

When you installed VS2015 did you include the C++ Programming Langauage and the Common Tools (not included by default)? You can check both of these by running the install .exe for VS and choosing the Modify option when propmted. Check the list of features and make sure that Programming Languages->Visual C++ and the entire Common Tools are checked before updating.

Cheers