Closing Mainframe window

Hi,
My mainframe window has close,mini amd maxi buttons.
But it does not work.
I cannot close or minimize the window.
Whats the reason.
My Precreatewindow codes like

BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
{
cs.style = WS_POPUP | WS_OVERLAPPED | WS_CAPTION | FWS_ADDTOTITLE
| WS_SYSMENU | WS_MINIMIZEBOX | WS_MAXIMIZEBOX | WS_MAXIMIZE;

return CMDIFrameWnd::PreCreateWindow(cs);
}
Whats the reason?

The code you posted show nothing except the CMainFrame window styles you want to supply by creating it.
Do you handle some of the WM_SYSCOMMAND options?
Do you change window style somewhere after window have been created?
Could you post a small text project demonstrating your problem? (please, post a zip archive but don't insert .ncb, .aps, .opt files nor Debug/Release folders).