Hello Decode,
Does your friend get any error messages? Does the launcher successfully shows up, or the game closes after he pressed the start button?
Firstly your friend should to download and install the
latest path to the client's installation folder, then open Autoupdate.exe there, which make sure the client files are not corrupted.
Secondly your friend should to install some general softwares that the client's environment needs:
After these steps your friend can try to check the general problems and their solution:
here,
here and
here (though maybe outdate information)