Error 23 fatal disk ...
This may or may not be helpful: http://www.wiki-errors.com/err.php?wiki=23
You could try a -repair of the client: https://help.guildwars2.com/entries/28148006-Repairing-the-Game-Client
(edited by Inculpatus cedo.9234)
This could be bad news for you but… you have two options:
1. If the game data files are corrupted (unlikely), reinstalling (re-download, important!) the game should work.
2. If your HD is corrupted, scandisk (right click, properties, tools, error-checking, scan for bad sectors) should tell you if it is, and if it is, it should be able to fix it.
If that’s the case it’s good to start looking for a new HD to backup your stuff…