First you need to remove any versions of Dark Age of Camelot that you want to reinstall by using the Add/Remove Programs option in your Control Panel. Once you have removed the appropriate versions of the game, go into My Computer and find your Mythic installation folder. Please delete the directory related to whichever client you are reinstalling. By default, they are in the following locations:
Shrouded Isles: C:\Mythic\Isles Trials of Atlantis: C:\Mythic\Atlantis Catacombs: C:\Mythic\Catacombs Darkness Rising: C:\Mythic\Darkness Labyrinth of the Minotaur: C:\Program Files\Electronic Arts\Labyrinth
Next you will need to clear out the data directory for that version of the game. You can find the data directory at:
Windows XP: C:\Documents and Settings\<Windows login name>\Application Data\Electronic Arts\Dark Age of Camelot\<name of client, e.g. LotM, DR, etc>
Windows Vista: C:\Users\<Windows login name>\AppData\Roaming\Electronic Arts\Dark Age of Camelot<name of client, e.g. LotM, DR, Etc>
Note: The Application Data or AppData folders are hidden by default, so you may need to enable "show hidden files and folders" under your operating system's Folder Options in order to see them.
Once you have found the folder you need, please delete it.
Next, reboot and run a defrag on your C drive. To run the defragmenter, open up My Computer, right-click on the C drive and select Properties. Now click on the Tools tab and finally click on the "Defragment Now" button.
Now you are ready ready to reinstall the game.