Kubuntu 14.04

I was trying to find a standalone Flash player the other day, and I found a suggestion online to edit /usr/local/mime/packages/something_or_other.xml (after all my bumbling, the file no longer exists). I made a backup of the file, made the desired edit, and ran update-mime-database.

All my icons became blank icons in my System Tray, and I got mime errors every time I clicked a launcher.

So I put the original file back in place of the edited one and ran update-mime-database again. Everything was still broken.

Finally I reinstalled everything that had to do with mime. That restored my icons, and I no longer received errors when clicking launchers, but clicking a launcher starts up Kate and gives me the corresponding .desktop file to edit.

I have reinstalled kde(everything), but the launchers still won't work. I have removed the Quicklaunch widget and reinstalled it, but it is always the same. Can anyone help me?

As far as I can tell, you've blown up your desktop ini files (effectively) that were generated when the applications were installed. If you wanted to clean them all up in one pass, you'd probably have to create a new user and migrate the data over to that home directory.
The good news is you could just edit the .desktop files to give yourself new functionality with the same old icons (or just provide minimal mime information and make the pop-ups go away)
http://standards.freedesktop.org/des...t/ar01s05.html

There are only three entries in the .desktop files that are mandatory and they a key/value pairs
Type: which holds and integer between 1 and 3~Application (type 1), Link (type 2) and Directory (type 3)
Name: which holds a string (i.e.application name)
URL: which holds the URL

While a new user will show that there is nothing wrong with the system and create new ~./foo files ("hidden" files in /home/<user name>) it is not needed.

This is obviously the problem. There fore simply removing the affected ~./foo files and rebooting will do the same thing for the existing user. The needed removed files will be regenerated at bootup just as the needed default files will be created for a new user.

Removal of all ~./foo files will, on reboot, give the default settings for all of the install. Therefore it is a really good idea not to delete the files but simply create a new directory in the current /home/<user name> directory and move all the "hidden" files there. Something like /home/<user name>/Hidden would be an easy thing to remember what it is for.

Reboot and then you can use the /Hidden backedup files to recreate, one at a time, your settings. This is nice for things like playlists, the look and feel of applications and so forth.

I am not a KDE user so do not know what files would be the problem here. Should be associated with KDE so anyother files, for music players and so forth should not be part of the problem. There are a lot of things, however, associated with KDE, like their Office Suite that are probably not part of the problem but may be hard to judge correctly.

Therefore removing all ~./foo files may be the easiest way to go. It will give you the same results as a new user without bloating your system with another /home/user directory.

It is, I should point out, not that hard to remove a user either but sometimes it takes a bit of manual removal of associated files for the removed user. This is particularly true if the new user is created using the gui tool instead of the cli tools as is generally the case for new users created by a fairly new to Linux administrator.