попробуйте это:
public const int SW_MAXIMIZE = 3;
private delegate bool EnumDesktopWindowsDelegate(IntPtr hWnd, int lParam);
[DllImport("user32.dll")]
static extern bool EnumDesktopWindows(IntPtr hDesktop, EnumDesktopWindowsDelegate lpfn, IntPtr lParam);
[DllImport("user32.dll", EntryPoint="FindWindow", SetLastError = true)]
public static extern IntPtr FindWindowByCaption(IntPtr ZeroOnly, string lpWindowName);
[DllImport("USER32.DLL")]
public static extern bool ShowWindow(IntPtr hWnd,int nCmdShow);