I disabled my notification center but i want to re enable it again i followed this link "How do I permanently disable Notification Center in Mavericks?"
If you ran
sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool False, it actually disables Notification Center because it changes the permissions of the plist from 644 to 600. If you change KeepAlive to false some other way that doesn't change the permissions of the plist, the NotificationCenter process is still started at login but it is not relaunched if it terminates for some reason. To undo the changes, run
f=/System/Library/LaunchAgents/com.apple.notificationcenterui.plist;sudo defaults write $f KeepAlive -bool true;sudo chmod 644 $f;launchctl load $f.
If you ran
launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist, run
launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist.
launchctl unload -w modifies
sudo launchctl load -w modifies /var/db/launchd.db/overrides.plist, so you could also edit those files directly.