1. edit your registry(run>regedit>software>gravity soft>RO) for ragnarok search height and width set them to DECIMAL input value :
700 and 1000.
2.run your setup as admin and close.
3.right click setup.. click troubleshoot compability>troubleshoot program>click windows XP.
4.right click setup again troubleshoot compability>use recommended setting>ok
5.try run <3
usually this problem occur with windows 8 and 7