[DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

[DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
public const int SW_HIDE = 0;
public const int SW_SHOWNORMAL = 1;
public const int SW_SHOWMINIMIZED = 2;
public const int SW_SHOWMAXIMIZED = 3;


//Call function
IntPtr hWndTarget = FindWindow("TaskManagerWindow", null);
bool bRet = ShowWindow(hWndTarget, SW_SHOWMINIMIZED);