Finaly found how to do it.

startInfo->WindowStyle = ProcessWindowStyle::Hidden;

is still not working. So i have to do it with the showWindow function, but to make it work, i have to wait for the program window to be on the screen.

Here's the working code

Code:
ProcessStartInfo *startInfo = new ProcessStartInfo(srvPathName);
startInfo->WorkingDirectory = srvPath;
Process* p = Process::Start(startInfo);
while(!p->WaitForInputIdle());
ShowWindow((HWND)p->MainWindowHandle.ToPointer(), SW_HIDE);
Thanks anyway