This example uses WinIsWindowEnabled to check that the parent window is currently disabled before calling WinEnableWindow to enable the system menu window.

#define INCL_WINWINDOWMGR    /* Window Manager Functions  */
#define INCL_WINFRAMEMGR     /* Window Frame Functions    */
#include <os2.h>

HAB   hab;                   /* Anchor-block handle       */
HWND    hwndSysmenu;         /* System menu window        */
HWND    hwnd;                /* Parent window             */
BOOL  fSuccess;              /* Success indicator         */

/* Obtain the handle for the system menu */
hwndSysmenu = WinWindowFromID(hwnd,FID_SYSMENU);

/* If the system menu is disabled, enable it */
if (!WinIsWindowEnabled(hwndSysmenu))
   fSuccess = WinEnableWindow(hwndSysmenu, TRUE);