Windows: Fenster soll nicht aktiv sein

[unknown]

Was an dem Stück Dokumentation meinst Du zu sehen, was ich nicht sehe?

"This parameter is ignored the first time an application calls ShowWindow, if the program that launched the application provides a STARTUPINFO structure."

Also mal probieren ob
ShowWindow(conwnd,SW_SHOWMINNOACTIVE);
ShowWindow(conwnd,SW_SHOWMINNOACTIVE);
hilft.