The MapleStory has compatibility problems with Win 7.. Here are some steps to change compatibility settings on MapleStory to allow it to run on Windows 7, but this will not work for all users.
(1)Uninstall your MapleStory installation
Click on Start Menu->Control Panel->Programs and Features.->Double-click on MapleStory from the list, then select "Yes," when asked if you wish to continue.
(2)Download the MapleStory installation file from the following link.
http://maplestory.nexon.net/Support/Downloads.aspxOnce the download has completed, double-click the file to begin the MapleStory installation.
(3)Browse to an installation directory and click next.->Click on Terms of Use and click "Agree" to continue, then confirm your installation directory again and click "Install."
(4)Click on the Start Menu->All Programs->Nexus->then right-click on "MapleStory" and select "Properties."
(5)Select the "Compatibility" tab in the MapleStory Properties and click on the box next to "Run this program in compatibility mode for:," then select "Windows Vista (Service Pack2)" and click "OK." If this does not work, try "Windows XP (Service Pack 3). Also, make sure that "Run as Administrator" has been selected.