string myState=null;

Microsoft.Win32.RegistryKey myRegistryKeyApp = Microsoft.Win32.Registry.CurrentUser.CreateSubKey("<<Give Here Your Window Form Path>>");

myState = (string)myRegistryKeyApp.GetValue("WindowState");

if (myState != null && myState.CompareTo("Maximized") == 0)

//Window Is In Maximized State

else if (myState != null && myWindowsState.CompareTo("Minimized") == 0)

//Window Is In Minimized State

else

//Window Is In Normal State