Hello,
in Alfresco 4, the active configuration of user dashboards is contained in the Alfresco Repository under /app:company_home/st:sites/cm:surf-config and its sub-structures. You could reset the entire dashboard of the user by deleting the relevant page and component XML files. Or you could fix it by modifying them, if you have the necessary know-how. After you have done either, you need to clear the caches on the Share layer. The simplest way is through a Share restart (if you follow best practices for deployment, then Share is separate from Alfresco Repository, and this should only take you a couple of seconds).
Regards
Axel