By default, the installer will bring you to the graphical user interface unless you use the /i /quiet options, calling it from command line.
GLPI-Agent-1.7-x64.msi /quiet SERVER=<URL>msiexec /i GLPI-Agent-1.7-x64.msi /quiet SERVER=<URL>The latter seems to work more often than the first one.
NOTE
Don’t use PowerShell as commandline interpreter: it changes some environment context the installer doesn’t handle well.