[DjNDB]

It's possible that your issue is caused by having multiple prefs.prop files, which sometimes happens for unknown reasons.
There should be only one prefs.prop, and that's in the savegame folder:
Win Vista/7: %USERPROFILE%\Documents\Telltale Games\The Walking Dead
XP: %userprofile%\My Documents\Telltale Games\The Walking Dead\


Please check if there are additional prefs.prop files in the install folder
(e.g. \Steam\SteamApps\common\the walking dead)
or its subfolders.
If so, make a backup copy of the prefs.prop and delete it from the install folder.

If that doesn't help, make a backup copy of the savegame folder's prefs.prop, and then try copying the install folder prefs.prop to the savegame folder.