Can't even delete MS?

Open up a run prompt[Start Menu --> Run{if you're using Windows 7 just type it in the search thing on the start menu}] and try typing "taskkill /F /IM maplestory.exe" without the quotes. That should definitely make the game stop running. Although, since you've already tried restarting and I have no idea why MS would start on boot - there may be a deeper problem here.