I saw this from a thread..
1.) Right click Ragnarok Online's icon in your desktop and select “Properties".
2.) On the Properties window, under shortcut tab, click the "Open File Location" button.
3.) You will now be redirected to Ragnarok Online's installation directory. On this window, look for this file "Setup_Classic.exe"
4.) Once you have found the file, Run this file as administrator and make sure something is selected in the first two menus. If one or both of them has no options available (which will probably be the case) that means that you have a graphics driver problem.
5.) Now, click the Start button and select "Run".
6.) Type in "dxdiag" and see if it works and brings up a diagnostic program. If it does, go to 8.
7.) If that doesn't work then that means that you don't have Microsoft DirectX installed on your computer.(download it from Microsoft website)
8.) Run Ragnarok Setup_Classic.exe again and check if it now gives you option. If it still does not give you any options, then that means that you do not have working graphics drivers installed for your graphics card. You can download them from the manufacturer of your graphics card (or, in the case of some systems, from the manufacturer of the computer).
9.) In case you were able to see options on the Ragnarok Setup_Classic.exe, then that means you have your graphics issue solved. Try to run the game again.
*flies away*