My little program

Ive created (transformed) this little program to close every window with one click when i finished to work,surf etc...

I put a check for "C:\\Documents" to avoid that it close itself before closing other
programs.

It works great only for a little time it gives a black screen for a few seconds when closing the windows. It didnt do it before.
I hope i havent done something wrong.

Thanks for any input on it.

Code:

#include <windows.h>

#define ARRAYSIZE(arr) (sizeof(arr)/sizeof((arr)[0]))

BOOL IsAltTabWindow(HWND hwnd)
{
    LONG_PTR exStyles = GetWindowLongPtr(hwnd, GWL_EXSTYLE);
    // Start at the root owner
    HWND hwndWalk = hwnd;
    // appwindows treated as no owner, so don't try and find one
    if(!(exStyles & WS_EX_APPWINDOW))
    {
        hwndWalk = GetAncestor(hwnd, GA_ROOTOWNER);
    }

    // See if we are the last active visible popup
    HWND hwndTry = hwndWalk;
    while ((hwndTry = GetLastActivePopup(hwndWalk)) != hwndTry) {
        if (IsWindowVisible(hwndTry)) break;
        hwndWalk = hwndTry;
    }
    // tool windows are treated as not visible so they'll never appear in the list
    // fail them here
    return (hwndWalk == hwnd) && !(exStyles & WS_EX_TOOLWINDOW);
}

BOOL CALLBACK Enum(HWND hwnd, LPARAM lParam)
{
    if(IsAltTabWindow(hwnd) && IsWindowVisible(hwnd))
    {
        CHAR Buff[260];
        GetWindowText(hwnd, Buff, ARRAYSIZE(Buff));
        if(strncmp(Buff,"C:\\Documents",6) != 0) PostMessage( hwnd, WM_CLOSE, 0, 0 );
    }
    return TRUE;
}

int __cdecl main()
{
    EnumWindows(&Enum, 0);
}

IsAltTabWindow is wrong.
See Explorer source code....

What is "Explorer source code" ?