Forticlient 6.0 GUI does not open

Hello, I have just installed Forticlient 6.0.5.0209 on my Windows 7 workstation;

This is the 1st time I install and use Forticlient; Installation was ok, and ended with my workstation reboot, which is normal; after this reboot, Forticlient green icon was present in theTask bar, but, nothing happens when selecting the "Open FortiClient Console" option by right-clicking this green icon; same thing if I select the "About Forticlient" option same thing if I double-click the green icon itslef the only option which works is "Shutdown FortiClient" which results in the green icon disappearing;

I tried to uninstall and reinstall Forticlient (with reboot in between);

nothing changed

Any help would be appreciated thanks in advance