-use CCleaner or TuneUp
-delete your whole nexon folder from your C:, unless you keep a backup of all fresh CA files like I do (where you can just copy and paste over ur current files)
-go to nexon.net and use there downloader to redownload and install a fresh copy of CA (unless you keep a copy of the newest CA setup file, then just reinstall)
It should then work. if you get the, failed to update protection modules, this usually HS based, so you could also just replace your HS files with backups (if you keep backups), instead of reinstalling everything.